Fired after PIP with no severance, after filing complaint about new manager fabricating conversations

This situation has gone far beyond anything this community can say or do, and I'll echo the general consensus:

Talk to an employment lawyer.

Having said that I'll try to add some helpful things.

The EEOC doesn't seem to have much it could do, unless you can show that your dismissal was because of your race or gender or age or other protected category, rather than just an ahole manager victimizing someone he doesn't like. But worth a shot.

In any advanced nation apart from the US I think you would have a reasonable case of an unfair dismissal suit, but in the US those are very hard. On the other hand US lawyers are very good at making things difficult for a company until they pay you some money. I don't even know if the EEOC has survived the recent political purges and has enough staff to function.

This is too late for you, but might be useful to other people in your situation. While you are still employed, take copies of all the communications you have had with your manager, with HR, with any other people related to these issues or your performance in general. Keep them in a place where you can get at them after you are terminated. Also take copies of all your performance reviews.

Even now, write down everything that's happened to you in as much details as you can remember.Write down what communications you had, even if you can't remember the details. (Your lawyer can ask to see "email of such-and-such date from KK to HR" if you know it exists.) Keep copies of every piece of communication you still have access to, or have from now on.

Did your PIP actually involve quantifiable performance measurements that could be used to judge if you were performing adequately? Or was it just a vague "you're going to be on this PIP for a few months and then we'll fire you".

As many of the comments say, talk to a lawyer.

HR is never your friend.