Step Over/Into/Out shortcuts in Xcode (F6/F7/F8) are the really obvious ones which I hit many times per day. Play/pause/etc. with the Fn key are easier to hit without looking than the touchbar.

I prefer that they change labels in a context-sensitive way. For keys that I don't use that often the icon is a better trade-off than a tactile response. Sliders are useful as well.

Jetbrains IDEs and VSCcode have a ton of default shortcuts using the fn keys.

I'm happily tapping away with them on a 2020 MBA

I'm not the person you replied to, but I frequently use the play/pause key and also the volume keys. I occasionally use the function keys in my text editor too.

Ok yeah I guess I use volume sometimes.

That's a good question. I can imagine some people never using them because of their particular workflow and software of choice.

In my particular case, I use them all the time. Edit some SQL, press F9. Select some files, press F5. And so on.

I can't work without the function keys.

Do you use IDEs for debugging?