If you know you are competent in your job and your manager presents you with a bogus PiP DONT sign whatever you do and just walk off the job. Yes you are fired but you would have been fired anyway. The Dirty secret of PiPs is that in most cases the worker is set up to Fail (intentionally vague “offenses” and deficiencies with impossible goals for passing). Think about it if manager and HR really wanted you to improve why the need for official documentation and paper trails? The most insidious is that PiPs are often given to the most loyal hard working who can’t believe the company would screw them over to avoid paying severance these people go the extra mile trying to meet these impossible plan goals and they end up fired while their manager gets a bonus. Trust me I saw this happen at Walmart and if there is any mention of a performance plan you immediately quit Do not wait around for them to screw you over and Do not waste any more precious time effort and life working for a psychopath have some dignity and self respect and quit on your own terms
What @Qgx4woj-1hrx said. Seen this happen several times. Good, hard working employees being put on PIP. Makes absolutely no sense at all, except that it's a setup to failure. Just walk away.