These work in both X and Wayland, even though they are an X feature. X/Wayland will consult the standard file, but will also consult a file ~/.XCompose. A number of people have created files with extended compose sequences, of which https://github.com/kragen/xcompose is possibly the best-known. If you install or change ~/.XCompose, you must restart your session (log out and back in again) for it to be recognized.

I used to bind the Compose key to Caps Lock, but I've recently decided that Right Alt is a better choice.

Another commenter mentioned WinCompose, which I have used very successfully with Windows 11. On a Mac, you might try https://github.com/Granitosaurus/macos-compose, which is quite usable, provided you install Karabiner Elements for the remapping.