It is surprising XM is going his route. Legal must be full of dimwits now.
Rules for the unfortunate ones PIPed:
1) Do not quit, make them fire you, so you don't lose any claims & unemployment benefits
2) Apply for unemployment, all you need to say is that you performed your job to the best of your ability, made up poor performance is not being fired "for cause" in any way shape or form!
3) Look for legal counsel - there will be plenty fodder here for EEOC & courts, unless you get large severance and release your claims - sue them
Resources:
https://skloverworkingwisdom.com/stand-up-for-yourself-at-work-resource-center/performance-improvement-plans-pips/
https://www.constangy.com/employment-labor-insider/big-lies-the-checks-in-the-mail-and-i-can-fire-you-for-a-good-bad-or-no-reason
http://employeeatty.blogspot.com/2018/10/no-your-employer-cant-force-you-to-quit.html?m=1