I cannot open a hyper link in word any more. I get the message »Your organization's policies prevent this action from being completed. Contact the help desk for more information« (in German). What can I do? I don't have a help desk to support me.

Is this your own personal computer or a company computer?
Are you using Ctrl+Click to try to follow a hyperlink?

It is my own PC and, yes, I use Ctrl + Click.

May I assume that you are using a German-language setup of Office?
Is this all documents or a particular one?
Have you tried, in a new document, inserting a Hyperlink, and then trying to follow it?
What happens if you open Word in safe mode? Open Office apps in safe mode on a Windows PC - Microsoft Office

I use a German-language setup.
It is in all documents. It is only in Word, not in PowerPoint.
I tried new documernts.
Same effect in safe mode.

You can do an Online Repair. Before you do this, make sure you have your installation media and product key.
Repair an Office application - Office Support

I did a fast repair: the problem remained.
I did a long repair: the problem remains.

Could it be that there is an option that regulates such problems?

I want to thank you, Charles, for taking on my problem.

You are welcome Eric. I am stumped.