Hi,
there was a problem with old plugins.
For the future I wold suggest to list all active used plugins.
Then disabling all of them and the update the forum.
If eveything is ok, update the plugins step by step to see if something goes wrong.
@PitaJ
Thanks for yopur help. 👍
In the future I have to read the error messages more carefully.
The "bad" plugins were mentioned there 😉