Comment by PurpleRamen

Depending on the topic, there is probably no acceptable substitute; which means, maybe Facebook, Discord or an awful videos-site (TikTok, Youtube) could act as a substitute, but then you had to use Facebook or watch Videos and let's not talk about Discord..

Reddit has gobbled up all kind of smaller specialized forums over the last decade, and established itself as the primary point of interest if you want something outside the walled social gardens. All attempts to rival them seem to have lost, and now we are at the endgame, and nobody seems to be there any more, who could take on the fight for the niche-problems of us powerusers.