I’ve updated Matrix “Authorization Strategy” plugin from 2.6.11 to 3.0.
Now on the “Assign Roles” configuration page, all users/groups are prefixed by:
"No type prefix:" in red.
I’ve understood that the new plugin needs adaptations. (https://plugins.jenkins.io/matrix-auth/#releases)
I’ve tried to delete the users and add them newly. But as soon as I reload the page after “Save” or “Apply”, I’m back in the same situation.

With the hint from https://community.jenkins.io/t/matrix-authorization-strategy-3-0-no-type-prefix/1043
I added 'USER:' before my user entries - that seems to have fixed the problem.

Some hint on that in the GUI would be really good. (and/or on the version notes https://plugins.jenkins.io/matrix-auth/#releases)

Update: Unfortunately, it seems my account has lost the “Admin” permissions. Quite bad, locked myself out for the moment…
So the "USER:..." didn't solved it seemingly.

In home/config.xml I found:

...

In home/config.xml I found:

...
   <roleMap type="globalRoles">
 <role name="admin" pattern=".*">
  <permissions>
....
<permission>hudson.model.Hudson.Administer</permission>
....
</permissions>
 <assignedSIDs>
...
<sid>USER:jm044248</sid>
....

jm044248 is me - so I would assume, I should have the Admin permissions, but....