Somewhat relevant: can somebody share good mpv defaults (or some other interesting technique) for playing YT videos? I have managed to get it to work, but it still pauses a lot for bufferring. I wonder if there's maybe some yt-dlp, ffmpeg, etc. trick to pre-cache some segments or something like that. The reason to play it in mpv is not to avoid commercials (I have a paid account), but because I can then play it from my editor while fully controlling the playback - it works great for watching lectures and taking notes.

Either download ahead, or turn down the bitrate via ytdl format expressions; see the latter's docs for how to express your desires.