works here, can you share your system info?
In the latest public WIP the command will ask you from what object(s) to delete the mapping, followed by which mapping channel to remove when you have the mapping widget selected.
You might be describing a bug in the WIP where deleting the mapping doesn’t return the object’s mapping to Surface in the viewport display. This is filed as RH-72072 for future reference. If you assign Surface mapping instead of using Delete Mapping, it will update as you expect.
I agree that Delete Mapping should also just delete the mapping selected and not ask you to select the object again and specify a mapping channel if only one exists. I filed this as https://mcneel.myjetbrains.com/youtrack/issue/RH-72198