I tried pasting into an Editor widget with Cmd-V (on a Mac). it didn't work. I also see no way to select text and copy it.
This was discuss [here] and [there]
This commit is the last in a long string of changes that implement low-level access to the clipboard for all platforms. Editor support is next.
This was added in https://git.sr.ht/~eliasnaur/gio/commit/a4d0c3e.