If you prefer #vp9 over #AV1 format in #YouTube, you can actually choose it in this link.

Choose the "Prefer AV1 for SD" option.

(Why this?
Some GPUs can hardware-decode vp9, but not #AV01. The CPU gets used to playback in AV01, instead of GPU. So, better playback.)

https://www.youtube.com/account_playback