Have you looked at Karabiner Elements⁽¹⁾? It’s extremely capable; see a config like this⁽²⁾ for inspiration.
I have it, regularly updated, from my efforts 10-15Y ago to try to get a Compose key working on OS X.
I failed.
I just haven't bothered to remove and clean up again.
Yes I'm using it because I don't use a standard Apple keyboard with my Mac.
The issue is mostly the user interface design is mouse first, not keyboard first. Windows was more than a little better on that front.