I want to disable the “R” hotkey which toggles trackball rotation when I’m already in object rotation mode. How do I do this?
Do do this, you can remove the keymap from your preferences.
Open your preferences, go to the keymap tab, and search for "rotation" as shown below. Find the keymap for mouse/trackpad rotate, and remove it. That should remove the hotkey.
I'm not 100% sure that is the right setting, but i hope this helps.