Well, tried to upgrade. Ended with this error message:
OK
Executing update-pre-hooks script "02_cmk-update-config"...
-| Unknown error on pre update action.
-| Error: name 'Tuple' is not defined
-|
-| Please repair this and run 'cmk-update-config'BEFORE starting the site again.Processing pre update actions...
-| 01/04 Rulesets...
ERROR (exit code: 1)
Fortunately my CheckMK server is a VM and I’d taken a snapshot before the ugrade attempt. Just rolled it back and it works again. But for now I’ll stay on 2.1.