I really wanted a Joy Con case for my phone to use when emulating games, and I saw a lack of options, so I modeled one up super quickly, enjoy!

Print settings: 0.3mm layer height 15% infill

Support: Yes Support Pattern: Lines Support density: 20%

I printed this in Pla, but you could print it in PETG if you had an easy way of removing supports.

Also lay flat on bed and scale the Z height to 102% - 106% if you are worried about clearances on your printer.

I scaled the Z to 104% and after minimal sanding the joy cons fit fine.