Before I left Reddit, I used a plugin through the api to replace all of my comments with random gibberish and then delete them. Part of this was because (mandatory) fuck spez. But more importantly, it was to protect the anonymity of my account. After years of posting, there is likely enough personal information shared to potentially connect my Reddit habits to my online identity. I wasn’t planning on using Reddit again in the future on that account, but I left it open in order to maintain some security control over the account. I’m not really sure what to do at this point because I still consider it a security vector that’s a bit concerning. There’s no way I can manually edit and delete all of my content with the snail’s-pace reddit UI, and I have no ability to assure that my content will remain unavailable or at least not publicly displayed.
The API-based deletion tools usually have to be tuned to delete posts slowly enough to not trigger Reddit’s abuse detection. Otherwise, they’ll automatically undo bulk changes like that.
This is, unfortunately, the only way to guarantee that your posts stay deleted. My account was 15 years old. I still log in every few weeks or so to go manually delete more comments. It’ll be a while.