@n5s I am sorry for what you are going through.
Regarding payouts, I can only give my non-legal background anecdotal experience. Payout will depend on your local laws, your time at the company, circumstances etc.
If you choose to go court and challenge the potential dismissal and payout, depending on where you are in the world, it could take 1.5-2 years just for the first hearing - while you have 0 income from the company. However, if you happen to win that trial, you might just get paid as much as the initial payout that was offered.
Please consult an employment lawyer. Document everything that you are going through.
And yes, it is an absurd process. It is a dystopian ritual where mediocre managers with sub-par personalities run the show/PIP.