Hi Saguaros,
thanks for checking. It seems to work now. I re-created the menu item and by that, the URLs changed as well.
Two more question:
1) I can't get the template to display the passkey option in the frontend (login link on footer menu). Is there anything I would have to enable? the webauth plugin is activated and Passkeys work fine in the Joomla backend.
2) In the article view in Joomla 3, I used to show the author, the publish date and the number of views right below the title.

In J5, only the date (without year) and the number of views is shown and in addition the alignment is left instead of center. What's more, the little gear-symbol in the upper right corner that enables sharing and printing is missing in J5. Is there a way to fix this?

Thanks,
Michael