It already lets you have different settings for the internal en external keyboards by default. I use it just like that - vanilla settings on my MacBook built in and for the external keyboard I switch command and option, since it’s a windows keyboard.

I don’t want to be inflammatory, but the amount of baby duck syndrome when people say MacOS and Linux are unusable is crazy. Just try to go vanilla for 2 weeks before you install two dozen utilities.

The settings in System Settings.app are per-keyboard, so you don't need anything external for that.