1) YouTube is owned by Google and their entire revenue model is in alignment with how Google does things, which ublock origin interferes with.

2) Manifest v3 is Google’s, not YouTube’s, project.

Manifest v3 doesn't stop ad blockers. In fact the chromium team worked together with ad block developers to adjust the design of Manifest v3 to better allow for them to be implemented.

Yeah chromium “helped” AdGuard specifically insofar as they agreed to restrictions. There’s a filter cap. It dilutes the efficacy of adblockers.