Here are models for a 3D printed case for the wonderful Corne keyboard designed by @foostan. The top piece in this model covers up the OLED, so this isn't a good choice if you are using underlighting or the OLED.
The top of the case is defined in top.scad, which I printed upside down. The bottom of the case is bottom.scad. Both these are built from case.scad, which depends on screw.scad which provides the cutout for a fastener between the two pieces. One side of the case has an M3-sized screwhole, and the other has a holder for a nut. Melting a small spacer into the plastic would probably be better.
In this version, the clearance for the TRRS and USB-C cable are both quite low, so it is a tight fit. I like the snug fit (since I don't want the TRRS cable to slip out!) but you may want to make those cutouts a bit wider.