Dear Ulli1,
It seems that I can't reproduce the issue from your description.
From example, I have the list with the Category column sort in the alphabet order.
Then I filter by Need.
Finally I add the new item Sprite, the Category column is still in the alphabet order.
So if something is misunderstood, could you give some examples about your requirement and show us some screenshots about the reproducing steps of the issue in your environment for our confirmation?
Note: Remove any private information before uploading the screenshots.
Thanks for your effort and time!
Sincerely
Cliff | Microsoft Community Moderator