Mercury Playback GPU not available.

Hola, aunque no nos comentas que tippo de tarjeta grafica estas usando, deberias actualizar los drivers de la misma directamemnte desde la web del fabricante, es la manera mas segura y confiable de tener al dia dicho contraolador.
Espro poder haber sido de ayuda.

Salu2

Please tell us the exact GPU and GPU driver version that you are using in your PC. It might be that you are using a GPU or GPU driver that is too old to be compatible with newer versions of Premiere Pro, or that your particular GPU does not have enough total VRAM on the card. Since Premiere Pro 2019, 2 GB of VRAM or more is now required (4 GB or more recommended). Your GPU may have only 1 GB of VRAM - not enough to even enable GPU acceleration at all in newer versions of Premiere Pro.