I found a cool trick
If you go to your forum posts you get a url like this
lichess.org/forum/search?text=user%3Athibault
but what you can do is add this to the end of the url
&page=[page number]
Keep increasing the page number until you get no forum posts, this means you went too far.
I was able to do this to find thibault's first forum post
lichess.org/forum/search?text=user%3Athibault&page=515
lichess.org/forum/lichess-feedback/show-games-in-the-forum#1
You can do this to any account.
This doesn't work for any post after 10,000 (You can't go beyond 1,000 pages)
If you go to your forum posts you get a url like this
lichess.org/forum/search?text=user%3Athibault
but what you can do is add this to the end of the url
&page=[page number]
Keep increasing the page number until you get no forum posts, this means you went too far.
I was able to do this to find thibault's first forum post
lichess.org/forum/search?text=user%3Athibault&page=515
lichess.org/forum/lichess-feedback/show-games-in-the-forum#1
You can do this to any account.
This doesn't work for any post after 10,000 (You can't go beyond 1,000 pages)