Are People with Bipolar Considered Neurodivergent?

Natasha Tracy, I have enough to say in response to this opinion piece that I could write an entire paper, but I have neither the time, patience. And it seems some important points have already been addressed in some way, such as the need to know and understand the history of the terms you are speaking about, as well as the history of the ways that standards of normal and abnormal, ie disability, came into being.
You seem to speaking solely from the point of view of the medical model of disability—e.g. viewing disability and neurodivergence as a "deficit"— as opposed to the social model of disability, in which people view disability not through the lens of medical deficits from an arbitrary, historical, and outdated standard of "normal", but through the lens of understanding that the social world has been created entirely based on this standard of "normal" (which, btw, is quite literally a white male with certain physical standards - read your history).
This is where the idea of accessibility comes in - in the social model, people with disabilities aren't in a deficit, but the way the world is built is acknowledged as the deficit. There's nothing inherently wrong with a circle, but you might think there is if you are told it is supposed to fit into a square hole.
And you never address these models or paradigms, which are crucial to the topic about which you are writing. You don't need to write a dissertation on them, but if you are so concerned with definitions, then arguably you would be concerned with the ways those definitions hold a great amount of ambiguity unless they are placed within their appropriate spheres of context. A sentence or two would clarify this.
Finally, "But I have this weird thing about definitions and using words correctly. And according to the definition by the smart folks at Harvard, those with mental illnesses or severe neurodevelopmental disorders don't qualify, and, in my opinion, it minimizes the experience of these people."
What minimizes the experience of "these people" is the ways that the smart folks at Harvard either ignore or talk at them because they are working from a medical model.
I'm also not saying that the medical model should be the only model, but anyone who is going to talk about this in an intelligent, just way and who wants to do their best to take into account all experiences is going to acknowledge these different models and worldviews.
TLDR; You cannot talk about neurodivergence without talking about the paradigm shift from the medical model to the social model.

The term neurodivergent was coined to include bipolar disorder. Neurodivergent is anyone who has a different functioning to their nervous system than neurotypical people. The term also includes people with epilepsy and chronic pain and depression.
Neurodivergent is NOT a scientific, medical or psychological term. It is a term made by a disabled person to describe the difference people with neurological disabilities face, in comparison with neurotypicals and/or those with physical but not neurological disabilities.
Bipolar people are neurodivergent. Neurodivergent simply means your brain and nervous system functions in an atypical manner.

I've been diagnosed several times in my life with bipolar disorder type I. The symptoms that have brought about such a diagnosis run in one side of my family and have resulted in several deaths and institutionalization.
I've done well in life. I exceeded at academics. I'm considered an expert in my field and I'm rewarded very well economically. I've never hurt another person outside of a few misunderstandings. In those cases I've worked hard to learn from my mistakes and to rebuild broken bonds with the people impacted in my life. My romantic relationships have been mostly fulfilling by social norms and have lasted well above the American national averages. I'm a father to a wonderful, healthy child.
For the 25 years since my first diagnosis, as a teenager, I've hid it from most people. I've avoided treatment with the exception of three episodes I could not handle on my own. While the traits associated with the disorder allow me to exceed at my job, the one time I finally needed to declare it at a disability to be on medication temporarily, I was forced to leave my job because it made others aware of "why" I exhibited what would be considered non typical behavior. Even if that behavior benefited said employer for a decade. I've put aside many aspects of my life that are important to me because "hiding" takes up too much of my time. I will not find "my people" despite a wide network of associations because social anxiety cripples me from forming all but the shallowest and deepest bonds with others. I've repressed aspects of my sexuality until the age of 40 despite being married most of my adult life. I have struggled with substance abuse for nearly 20 years. I've had suicidal thoughts for 25 years and the only times I've come close to acting on them was under the influence of mood stabilizers.
I'm not disabled. I'm wired a little differently. The downsides for me - some substance abuse to help me sleep and avoid a major episode, abusive exercise and brief periods where I find it difficult to regulate emotions - let's say they shave ten years off my life naturally. None of these things are even out of the norm in American culture. Many people drink more than I do. Run harder than I do. They might struggle with anger. But it's accepted. The moment someone knows that those aspects, for me, are associated with a condition that is involuntary, cyclical and that can escalate under certain circumstances if I don't listen to my body, I'm disabled. The social anxiety isn't an outcome of bipolar disorder. It's a side effect of not being comfortable being myself around most people because I am aware of the traits and behaviors that will be seen as atypical. The suicidal thoughts aren't due to a brain chemistry imbalance. They're because hiding and acting for most of your life is emotionally exhausting.
When someone is atypical in their behavior according to social norms and they can't hide it, we label and isolate them. In western medicine we used to label women demonstrating sexual desires as "hysterical". So this is nothing new. Those of us who are aware enough of both how far from the norm they are and how they'll be treated as a result manage it by hiding. Those aren't lucky enough to hide, deal with the social downsides and poor outcomes associated with their "disorder" because they're rejected by the people around them.
Why this terminology of neurodivergent matters to me: I'm the third known generation in my family demonstrating similar characteristics. Much of my fulfillment in life, or lack of, has been shaped by fear of how I'll be perceived and how that will affect me. Even though I'm normal. I'm not deficient. I can fit into society. I can thrive without medication. But the fear is with me at every moment. Because of how others see me when they are aware of one of my labels.
This terminology is important to me because it gives me hope my daughter will not live with this same fear.

Remove modern capatalist societal expectations, and much of what some might call 'deficits' falls away.
Variations in neurotype are long-standing, likely evolution-benefitting qualities for human communities.

You are also only looking at the negatives. What about the positives. As a functioning bipolar II person, I regularly experience periods of hyperactivity, that if I manage carefully, which are brought on by a busy job, can help me be exceptionally productive, precisely because of the way I interact with the world. Surely that makes be neurodivergent?
Oh and as a software tester, I believe my attention to detail is also enhanced by the way my brain processes.
and hope you don't mind the feedback (I am a tester) ;-) the sentence "People who think, learn, and behave are known..." is missing 'in a standard way' I believe.

I guess my OCD and ADHD-I symptoms qualify to be neurodivergent, but my BP1 with psychotic features and rapid cycling in remission don't qualify me for being neurodivergent. I may be on the ASD spectrum, but I don't know.

Just because you don’t agree with a choice to not view differences as deficits doesn’t mean the term neurodiversity excludes those with severe disorders. The “smart folks at Harvard” didn’t disqualify those with mental illnesses and severe neurodevelopmental disorders. You did.
And, yes, using this label to fight for inclusion in the workplace doesn’t help those unable to work. So? Please describe your plan to transform the workplace to help those unable to work. There’s no such thing! People unable to work aren’t in the workforce.
People who are unable to work have their own unique problems that I hope well-informed and well-intentioned people are working to solve.
But why stop the efforts to make professional environments better equipped to support people whose brains function differently than the average person?
I’m a professional in my mid-40s with a collection of differences that qualify me for the neurodivergent label. I have accomplished and contributed a lot in my career, but it has been very hard. Mostly because of the ways my brain differs from others. There was no support for me to figure out how to deliver results, but there could have been. I could have contributed even more with less stress and pain.
Life will be less challenging for people like me if it becomes known that neurodivergent people have a lot to contribute and the value we add is worth the accommodations they may have to make to get the most out of us.

Calling yourself neurodivergent does not mean denying you have a disability. And Harvard does not get to decide on the definition of neurodiversity since the term was actually coined by a sociologist named Judy Singer--here's a nice website on her: http://www.myspectrumsuite.com/meet-judy-singer/ . Neurodivergence was rooted in the autism community--it's only recently that people with ADD are also using that label. I've heard autistic people saying that bipolar should not be considered part of neurodiversity but this seems to relate to stigma as though they want to prevent being associated with mental illnesses. BTW, I think you left out some words in your definition: "People who think, learn, and behave are known as neurotypical"