Zardnaar
Legend
When I ran 5E, very rarely / never. Sturgeon's Law. 90% of everything is crap. I have a hard enough time keeping out the official crap. I don't have time to go through hundreds of 3PP books to find the 10% that might work for my table. If any of the players want something new or different we homebrew it ourselves.
When I played 5E, one DM let a player use a "song dragon" that's some kind of were-dragon thing. The DM didn't bother to check the stuff before the player, mid combat, changed into a massive dragon, breathed some kind of nasty on the enemies, and ended what was supposed to be a deadly encounter in a single action. That was the last time 3PP content came into his game.
This is why I only allow curated 3pp from trusted sources.
Archetypes are fairly safe. New classes not so much.