I use freetube which doesn’t have a algorithm so avoids that issue, and let’s you block channels from appearing in even searches.

But, if insistent on using YouTube.com turning off watch history gets rid of recommendations and blocktube extension allows for channel blocking.

Never had luck with don’t recommend this video to me option even though Id go out of my way to avoid visiting any of the videos posted by certain channels. They’d still after a while post the channel content in recommendations, since I guess they are highly trending.