Hard Requirements:
NOT Mastodon. That's simply a different paradigm. NOT tech only. Wide spectrum discussion. NOT an alt-right hive.
Soft Requirements:
A decent mobile interface, preferably a non-crappy iOS app. Not overtly commercial/meme/crypto oriented
Lemmy is the only alternative I have seen so far that has learned from the failures of Voat.
But the userbase is tiny, and smaller than even niche subreddits.