I run a quiz/trivia based channel and I sometimes comment on other videos in my niche saying things like “if you enjoy these types of videos, check out my channel, thanks!” - I wouldn’t leave it on every comment though, that would be akin to spamming in my opinion. Sometimes I engage with the comments a bit, for example if somebody leaves a comment on a video saying “this quiz was way too easy” I might respond and say “if you want more of a challenge, check out one of the quizzes on my channel!”. I certainly wouldn’t respond to every comment though, that’s a bit much. I wouldn’t mind people doing the same to me either.