@ajbz There's literally a couple of decades of games for you to dig into, which are GM-less and have a vast multitude of different ways of approaching that, even before we get to the question of only multiplayer or solo/co-op, which have become extremely popular over the last several years.
The right place to start these days is probably with #Ironsworn, which you can get your hands on for free. And if it tickles your pickle, you can pick up Ironsworn: Delve, which goes into some more detail on how to dynamically generate exploration environments, including dungeons.
But, there are a ton of GM-less options out there.