There’s no ‘designer’ case for any of the Fairphones, the best you could hope for is a generic waterproof housing, for the beach etc. or heavy rain when attched to a bike’s handle bars.
The soft case however is effective in protecting against drops, it is flexible and takes more impact than a solid case.
By the way this about users ideas on what they want out of the FP5 there are topics that deal with cases and the FP4, so I have asked your query to be moved.
Until then search for such and I will also look and provide links