Its a good tool for automating this process but why do I have to create a timeshift? I mean when I break my system (unfortunally this is often) it does in most cases not even boot so a timeshift does not help at all...

Great, no issues with the upgrade manager. However this would have been even better if one could get an alert somewhere in the desktop bar or in the update manager to let users know that a new Linux Mint version is ready to upgrade with the upgrade manager.

It worked quite well, but with a glitch. Here's the glitch and the workaround. the Google/stable package (in the third menu item) did not have a public key, which brought mintupgrade to a screaehing halt. I unchecked it and was able to proceed. When it checked for orphan packages, there were a bunch. The fix was to check the Google/stable package again, and click Fix.