Do I need to get 100% of everything if I want to submit a Glitchless run?

No, you just need to reach the end of the game as fast as possible while avoiding what we consider glitches, you can find the details if you press "View Rules" on the Glitchless leaderboard.

Getting everything in the game would be a 100% run, that's its own thing (but we don't have a 100% Glitchless category specifically)