500 chars are a bit low sometimes.
Then a micro-blogging app is probably not what you need (hammer>nail). That said, a bunch of the other fediverse apps don’t bake in char limits, leaving it up to the instance admin to decide if they want to set one. Maybe what you’re looking for is something like Hubzilla, whose UX is designed around blog length posts? It federates with Matodon over both OStatus and ActivityPub.