The problem is that the OP didn't request accommodations until HR had already scheduled a meeting, which the OP assumes was to fire them:
> I suspected they were going to fire me (scheduled 1am call with HR) and I've decided to share with them 3 days ago my Bipolar Diagnosis.
The OP also explains that they were not communicating with the company leading up to this event.
Unfortunately, the ADA accommodations can't be retroactively applied after the company has fired the employee.
Unless I'm misunderstanding the OP's post, we shouldn't be encouraging them to pursue legal action which is unlikely to produce a positive result.
You said diminished communication is grounds for dismissal. You didn't say diminished capacity might excuse it. Both are important.
It isn't clear if they disclosed the condition before or after the meeting was scheduled. It's clear they did it before they were fired.
They said their communication dropped. They didn't say they weren't communicating.
We should be encouraging them to get advice from a qualified professional.