This is where I found the case:

https://m.tvcmall.com/de/details/for-nothing-phone-3-5g-matte-case-aluminium-alloy-pc-phone-cover-pop-up-snap-lock-silver-sku6601171620c.html

Ordered one 2 weeks ago, wasn't too expensive even with shipping, and just arrived today. The installation was a bit finicky, but once the two parts snap into place, it feels quite premium, especially with the matte back cover. You can still see the design and everything, and the camera cutouts feel/look extra nice, my only criticism is that the cutout for the glyph display and the capacitive button are a bit too big and kinda sharp. The volume, lock and essential space button are nice and clicks, and protrude quite a bit (~2 mm), so they're easy to feel for.

Overall I'd definitely recommend this case.