Windows needs to just adopt this rather than punish users with the alt codes. Compose key is so much better than dicking around with an IME or dead keys.
I actually find dead keys quite practical. MacOS uses those, and it allows me to easily type French on a US keyboard. This also allows you to easily type other symbols, like •, º, etc. Maybe not everything, but it's fine for my needs.
I've spent quite some time to figure how to make Linux do the same. Turns out it's rather easy: just set the layout to macintosh, and remap some key to "level 3 shift".
I've actually went all in on the mac layout, so I've remapped the win (left) and menu (right) keys to this, so it's in the same spot as on the mac, which helps with muscle memory. Since caps is useless anyway, I've moved super there.
Now this is a bit more involved on Windows, but it's doable. There is a "macintosh" layout available on github, and it's possible to remap the keys using the registry as on Linux.
Russians solved this almost 20 years ago with two (one for Russian and one for English) custom layouts where right alt is used a separate typography layer.
I have made a keyboard layout for Windows that abuses dead keys
and AltGr as a substitute for compose key, the difference being that such compose key needs to be held while typing the first character:
