Shortcut: Add treble/bass clef

You can redefine this shortcut to something that is better for you in Edit>Preferences>Shortcuts:
Clear the shortcut for Add Treble/Bass Clef, and define the shortcut to something that is better for you.

If you use Windows, you can also look into this forum post (https://musescore.org/en/node/303798), which describes how to create shortcuts for any palette item using AutoHotKey (which is free).

You can also customize your palette to hide all the crazy ones you don't use. Or create a whole custom palette with just the symbols you do use a lot - even things taken from different palettes - and then just leave that one open.

Yes - I have this problem too. It works as long as Redo is disabled, however. But as it turns out, not in the upcoming version 4 development build (MU4) - in fact in MU4 there are no "add clef" commands you can map shortcuts to yet, presumably this is just yet to be implemented.
But the reason I was trying it out is because the behaviour in MU3 is very odd - it doesn't add the clef at the same point it does when you add from the palette. I can't work out exactly where it's trying to add the clef, but it's definitely not at the measure I'd selected - in fact it seems to be before whatever individual note/rest I'd previously selected, even though I've now made a totally new (range) selection and there's no visual indication of what was previously selected.
Adding clefs from the palette works as expected though.