Is there possibility for No Item categories to be added for certain events? Or would that make the page too cluttered?

Idk about no Item categories because it's too restrictive for the most recent events.. I think It'll will better if it will be No Attack-Up Items Insteaf

You could do a no items run if you want to add a difficulty to your runs but i won't add that as a new category since some people already do no items runs as a regular run