There is no official Roblox on PS5 release, but that doesn't matter as you can use the PS4 version, so here are the details for how to set it up.

Roblox is coming soon to new platforms like the PS4 and PS5, opening up its creation tools and community for many more players around the world.

You can play PC games with your PlayStation controller, but it only works with some games by default, while others will require workarounds.