Designing a simple photo frame. I wanted to make it so that it prints without supports. While printing, however, the back support part wobbles/vibrates with movement, and is printing terribly.

Ender 3v3 CoreXZ, PolyTerra matte black filament, using the CR-PLA Matte profile in Creality Print 7. Tried printing at slow speeds, the issue still persists.

I've tried making the back support with only 45 degree angles (previously it was an x diagonal), made it thicker (from 0.75mm to 1.5mm). Nothing is working. Please find the stl and 3mf here (https://www.thingiverse.com/thing:7281179).

Is this a printer issue, a model issue, or a slicer issue? Please advise.