yeah if the lawyer thinks there is enough to go on to build a case, OP could sue. But the case might not be strong enough and OP might not be able to take that legal risk on. Usually you can get legal fees in your severance but only if you win. And if not you have to pay a lot so it’s a risk assessment based on if the lawyer thinks there’s enough to go on to straight up sue. Company could come back with “performance” examples that weren’t a big deal at the time but will be presented as such.

More likely the lawyer engages with company’s legal and they come to a severance agreement over some back and forth email negotiations - unless OP already signed and agreed to the terms of being let go might be a harder. But still possible. The lawyer will present what OP feels transpired and what’s fair and legal will decide what to do

But I’m like 99% sure that a letter will be no problem (plus likely $) so at least OP doesn’t have to worry about that.

It sucks but employment is at will. Anyone can quit or be fired at any time for no reason given. This can make suing challenging at times. I’ve seen some crazy things - people getting paid when it made no sense and people getting nothing when they should have. Definitely try but my advice is get the letter and look at what’s next in your career and don’t go on a rampage and burn extra bridges cause industries are smaller than you think.