The YouTube app on my Android has a straight up "Don't recommend this channel" button that does what it says on the tin. Honestly I use it pretty sparingly.
Im on iphone and use that all the time not that OS should matter. It doesn’t do anything. It will recommend the channel to me the next day half the time.
Weird. There are a couple channels I'm sure it would recommend to me incessantly if I hadn't blocked them.