Snap/Flatpak/etc. often mean you can't use IME (input method extensions) with programs packaged with them unless the packager has jumped through certain hoops, which they usually haven't.

Ew, that's... extremely unfortunate. I'm sure there's some internal reason, but that feels like something the system should be able to add support for unilaterally, at least by default, without needing special packager effort:(

You can use the character map however, as character map copies the output to clipboard.