I couldn't find a M5Stamp STL file anywhere. The only thing I found was an .stp here:
https://github.com/m5stack/M5_Hardware/blob/master/KiCAD/M5KiCad/M5KiCad.3d/M5STAMP-S3.step
So I grabbed it, opened it on prusaslicer, and exported it to STL.
I didn't make this design, just converted it. I'm uploading it so you save the time I spent finding it and converting it.