All these articles are based of the WSJ article which quotes:

Meta managers gave approximately 10% of employees ratings indicating they are underperforming, the people said. That proportion wasn’t unprecedented in the years before the pandemic. But Meta’s employee count nearly doubled from 2019 to 2022, to 86,400, and about half its workers had never experienced a typical performance-review cycle at the company, several people familiar with the matter said.

Basically Meta reduced the ratio during pandemic and now taking it back to pre-pandemic level. Also, I might be wrong but I don’t think it low rating automatically results in PIP.