Making a simple tweak like setting caps lock to an extra ctrl is a whole side quest on Linux and you may never really get it working everywhere.
I've remapped CapsLock to Esc on both macOS and Linux/GNOME. It's just a checkbox/combobox in a settings in both cases. What is 'a whole side quest' you are talking about?
Whereas in Mac OS X it's a simple configurable option (a bit hidden, System Settings, Keyboard -> Keyboard Shortcuts -> Modifier Keys).
I know there was a way to load different keyboard layouts, but the problem with those mechanisms is they often cannot remap modifier keys, of which capslock is a special case of.