thanks for looking into it. I don't see any misconfiguration either. However, I am clueless where these 404 calls are coming from as displayed on the image avove.
Mind that these are logged attempts where Joomla's native Components > Redirect keeps a record of when someone (or something) tried to access a certain URL and failed.
The invalid URLs could be caused by a browser with a wrong encoding. Or it could be a search engine or another automated attempt where the entity trying to access the page was not able to properly put the umlaut in the URL.
I wouldn't worry about that. The is not issue with the Tags. You can test it yourself.