A great privacy focused client for YouTube is FreeTube. Uses a native API or Invidious for playback, and you can download and share videos from it. Doesn’t give any identifying info to Google/YouTube and I’ve never once dealt with an ad. For mobile, Grayjay and NewPipe are similar apps.
IIRC Mozilla doubled down on their v2 support when Chrome announced the shift to v3. But then the Chrome monopoly judgment came down and with it a lot of speculation on Google dropping their funding of Mozilla, so maybe Mozilla could be changing its tune to either protect or find a replacement for that funding? Nothing of substance is happening yet, it’s still all speculation, but I do hope nothing like that does happen.