Here you go. Feedback requested please!
I'm no JavaScript programmer, and it's a bit hacky, but it works.
No fancy UI, just edit the list of usernames to block.
I welcome people improving on it!
There are 2 types of blocking:
1) post is hidden - clicking brings it back.
2) post is deleted. can't be brought back.
"2" probably seems a bit of a puzzling addition - the original idea for that was to make such posts completely invisible with no mention of them, but I found in testing that this made peoples replies to said posts appear to be replies to the post above, so I needed to put something there to show a post was deleted. Ideas for alternative solutions welcome.
First version release: https://www.jamiejones.org/tampermonkey/Filter%20Users%20on%20The%20Register%20Forums-2025-02-09.user.js