Update: I am using a “bumper” case since a few weeks as daily driver. The filename was “silicone_bump_case.stl“ but I can’t find the reference anymore atm to give proper credit. Here are some pictures (shot on Oneplus 6 via pipewire/gnome-snapshot in bad lighting conditions):
I find it much better than the previous one (where some noses broke). What I also learned now from the docs is that the newer Librem5s are longer (153 vs. 150mm) which explains why I had problems with fitting it in both cases. The opening for the USB port was a bit too narrow but it was no problem to make a cutout with a knife. Also the 3.5mm jack probably needs a cut, too.
Printed using FDM and black TPU with 30% fill.