OK, let me know.  I do suggest an external SSD instead of internal for scratch disk an unchecking the system drive, but for a different reason.  SSD drives have a finite lifespan.  I don’t like Photoshop wearing on the system drive by continually writing hundreds of GB or even +1TB at a time to it.  Although, I’m not sure if it is actually writing all of it or just “reserving” the space in some cases.  However, the SSD can’t be replaced on an M1 because it is on the M1 chip itself. So I would want to not abuse the SSD if I didn’t need to 🙂