looks like my Problem - what wasn’t the Nextcloud Core but the old social APP.
If you don’t use the social app
delete it
try - deletes the social app
php occ app:remove social
try - deletes all config settings from that app
php occ config:app:delete social all
try the updater again
php occ upgrade
If you don’t use the social app
if the upgrade still fails
delete the database tables oc_social_3_* and oc_social_*
or do it step by step - index by index if you try to save the social app data - if any exist
Index name “nid” for table “oc_social_3_stream” collides with the constraint on table “oc_social_3_cache_actor”.
so drop the index “nid” for table “oc_social_3_stream”
re-run the updater - look at the next broken index
and drop the next index for that social plugin table
in my case there where ±20 broken indexes to drop until the updater runs flawless
what damage one beta app can do…