I am interested in speedrunning this game and I don't what to play it on.

download the red ball definitive collection in resources

how do u use the definitive edition?

go into "Resources" and download the definitive collection. If you're confused on how to play it then, then check out maximum's "beginner red ball guide" (the new one) (he talks about how to use the standalone in the guide).

Thanks yall. I will probably do a speedrun tomorrow.