If you create document and add a new field and set that type to "int32" or "int64" the GUI flags the update as an error. Even if you enter a valid number. There is no way out of this error without changing the type back to a string. Entering the number and then changing the type to int32.

See the attached screen capture (server 4.0.2).

Orginally cited in https://stackoverflow.com/questions/61853674/mongodb-compass-throws-error-update-not-permitted