The main way I watch Youtube is through a Firestick on tv. During the last election cycle there were nonstop unskippable ads from Citarelli's campaign: 'HEY, its Jack, did you see my ad yet?'

For browsers the blocking is easy with ublock origin or adblock plus, for these (firestick/android dongle) devices you need to use a 3rd party client if you want to avoid ads, SmartTubeNext is good, setup guides are here: https://smarttubenext.com/

I also use Newpipe on android, unfortunately there's no non-sketchy options for ios unless jailbroken. I guess you could open videos in https://piped.kavin.rocks for adfree (also supports playing in background).