Malolo's screw-less / snap fit Raspberry Pi 3 Model B+ Case & Stands by Malolo
Creality CR6 CR-6 SE Under-screen / Side Rail Raspberry Pi Model B 1 2 3 Case" by SANGER_A2
Top for 35mm Fan" by PBahner
You can find my remix at the link below, but I'm just now starting to print it and don't have a RPi to test it with currently (at least not without ripping apart one of my existing Pi cases). This may also work with the ender3 and some variants, if the 40mm aluminum extrusions are similar.
Update 8/18/2021: The design was printed on my buddy's CR6 SE and it turned out well, but it did pick up some residual material that was stuck to his bed, but since it's a functional part I think it is fine. I don't have a fan to test with it, but I have some 40mm fans on order.