I've been trying to avoid it, but I'm very close to giving up on macOS altogether. After a couple more hours of troubleshooting I've noticed that my mouse is also detected by macOS as a keyboard. You can see this if you open System Preferences > Keyboard > Keyboard > Modifier keys and look at the keyboard dropdown at the top. I'm hoping that by setting the same keyboard layout for my mouse (wtf Apple, really!?) it might work now. macOS is the worst operating system I've ever used 😂