I ended a run of Top Gear Co -Op but I have no idea, i have to play in all difficulties or not?

The leaderboards don't specify, so I would say it's 32 races of one difficulty, and your run will then set the precedent for all other co-op runs (until separate categories are made)

this speedrun is valid or not? (to submit)

I don't know, I don't run the game. Why not submit the run and the games moderators will accept it or not.

ok