Appears to be a very old garage. Could be the framing is a full 4” and a standard “4-inch” door was too small. That would explain why a 6” door sticks out 1.5”. I can think of 2 reasonable options.

1. remove the door frame and disassemble it. Trim off the excess 1” from the outside edge- furthest from the hinge cutouts. Reassemble and reinstall. Maybe that’s not so reasonable after all.

2. it looks like there’s enough room between the door and the light switch to simply box it out. Rip a stud to the desired thickness. 1” if it’s 1.5 out. Screw it to the stud closest to the frame, add from the frame into it. (This will make your door more secure. As it is, a not very hard kick is splitting the door frame open.) then drywall a funny-looking corner. If you can’t find skinny enough door trim- rip that as well.