Lots of software uses Fn key bindings by default. IntelliJ & mc come to mind first, but there are many others. Sometimes they can be remapped, but given the number of key bindings required by pro software, replacing roughly 1/5 of the keys with a silly little nontactile screen is a nonstarter for me. I never look at the keyboard (that's what the real screen is for). Indeed this was the precipitating factor driving me away from the Apple 'ecosystem' in 2018.