GNOME Disks aka gnome-disk-utility displays and manages disk volumes. It can also create ISO files and restore ISO files to USB sticks etc.
It is a libhandy based app. At the moment there are no issues raised upstream related to GTK-4 and/or libadwaita.
If there are any other apps that could in the future be a ready alternative please shout - but for the moment I’m content for this app to continue being a default app for UB.