I understand how to delete my YouTube comments, but is there a way to bulk delete all the replies I have made at all video sites without having to return to each individual site?
It is possible to programmatically remove comments, see this answer at Stack Overflow: "Remove a comment using the youtube data api v3?", but the quota will limit you to ~200/day.
Here is their help:
You can also go to this webpage: https://www.youtube.com/feed/history/comment_history and manually delete the ones you want, as many as you want, fairly quickly (and likely more than 10/minute, if you have patience).