While pretty much anything I patch via the PUT /rest/api/3/issue/xxx-route leads to an error when the patched field is not part of the respective “Edit issue” screen, when patching the issuetype, there is no error at all. I get a 200 response, but nothing is changed.
This can be highly confusing.
Please add a check and return an error when patching the issue type and the screen does not allow this.