If you have Everest installed, opening Celeste via Steam will open Celeste with Everest, not the vanilla game. You can either hold right on the title screen to reload into vanilla as ItzPriest mentioned, or another option is to download Olympus and use that as a launcher which includes an option to load directly into the vanilla game, amongst other features.
There is no real difference in the actual game*, at least in any%. Being on PC just provides runners with a few advantages, e.g.;
• More button binding options, such as creating a demo button • Access to debug mode & mods to make practicing a lot easier • Using keyboard, for those who prefer that method
So all of the top runners will run the game on PC
(* I only know of 1 screen in Farewell that is different on PC to how it is on console (it was made easier in a later patch consoles don't have yet))