From this thread (and elsewhere): https://github.com/utmapp/UTM/issues/3567

and confirmed here: https://github.com/utmapp/UTM/releases/tag/v4.6.1

The copy/paste issue with macOS guest host is resolved in v4.6.1+ only for macOS 15 host AND guest. "Copy/paste synchronization between macOS 15 guest and host now works when the guest tools are installed (from the CD icon in the toolbar)."

"Earlier guests are not supported due to a bug in Apple's VirtIO drivers."