In Android go to settings > apps > app management. You can then also revoke permissions.

To add to that, I reckon apps shoud show an example notification for each category. It’s cool and all that notifications got categories, and you can disable specific ones, but I’m still clueless oftentimes about what a category really is or what I am disabling, due to their simplistic category title. Does this disable something important, or just the annoying crap they send to try to get us back in?

I think that’s something Apple does, actually, where apps give explanations for every permission they ask for. No idea about allowing them later or if they state if they’re necessary though.