I'm on a YouTube premium family plan for free right now, because my sister had an extra spot open. Once my nephew grows up and I get kicked off, I'll switch to ReVanced or NewPipe.

Firefox nightly has all the usual extentions (ublock, sponsor block, and yt enhanced) so these days I just use that (with NP for downloads)

I did but more and more videos don't play anymore.

No, i only use Newpipe Sponsorblock

Yes the Revanced YouTube Music app

Si ce we are on topic, is there a way to have DeArrow on mobile? (potentially I could install it on FF, but would prefer an app for YT).

I use LibreTube.

Yes.

Also xManager, a similar tool for Spotify. I'd use revanced for YTmusic, but most people seem to use Spotify and it's nice to be able to share playlists with friends.

I have reVanced but unfortunately I struggle with getting it to work consistently. Most commonly, the video will play for a minute or so and then buffer endlessly. My Internet research tells me the only way to fix it is to root my device, and I'm honestly not willing to go that far. Luckily I have adblock installed on my phone, so the official app is tolerable.

All the time. At this point I'm waiting to replace my second hand iPad with an Android tablet so I can achieve a truly optimal YT experience.