I was just looking into this last week! If you want really active, constantly-updated stuff, Archive of Our Own is the undisputed central hub. The tagging system over there is a lifesaver, especially with a show that has a big cast like 'Disventure Camp'—you can filter for Fiore-centric fics, his pairings, or specific episodes so easily. I've noticed most of the quality, multi-chapter stories and the serious authors post there first. But honestly, you can't sleep on Wattpad if you're in the mood for something a bit more... chaotic and fun. It's flooded with reader-inserts, chatfics, and what-if scenarios that update super fast, though the search function is a nightmare. Tumblr is where a lot of the headcanons and shorter drabbles live, and people reblog and add on to each other's ideas, which builds a different kind of community vibe.
For a more niche spot, I stumbled on a surprisingly active forum on Fanfiction.net dedicated to the show, but it's mostly for discussion and linking to stories hosted elsewhere. It feels a bit old-school, but the regulars there are deeply invested in character analysis, which sometimes sparks the best fic ideas. My personal favorite thing to do is cross-check: I'll find an author I like on AO3, then see if they have a Tumblr for extra snippets or polls about what to write next.