I just upgraded Discourse and see a message now:
[Admin-Hinweis] Eines deiner Themes oder Plug-ins enthält Code, der aktualisiert werden muss. (ID:discourse.deprecated-resolver-normalization)
And in developer console:
DEPRECATION NOTICE: Looking up 'route:admin-plugins-fingerprint' is no longer permitted. Rename to 'route:admin-plugins/fingerprint' instead [deprecation id: discourse.deprecated-resolver-normalization]