Thanks for reaching out to Octopus Support, and I’m sorry you’re running into this error attempting to rename a project group.
Unfortunately, you are running into a known bug. More info on the bug can be found in this GitHub issue. The fix will be included in our 2023.1 release once it is made generally available. The workaround is to create a new project group with the desired name.
Please let me know if this helps or if you have any other questions.