Hi Gianluca,

It appears you have AutoCAD 2023 for Mac, and you have "Shaded with edges" Visual Style enabled.

If yes, then try to turn off FASTSHADEDMODE:

Command: FASTSHADEDMODE
Enter new value for FASTSHADEDMODE <ON>: off
Command: 

Now JPGOUT should work - see attached JPG

EDIT:

If you leave FASTSHADEMODE=ON, you can use PLOT command ->Preview and save PDF opened in Preview app as JPG