23 GB is very little. The message is real. Clear up space on your system drive, or get a new drive to use as Photoshop scratch disk.
Photoshop uses a lot of disk space for temporary working files that can't be held in RAM (scratch disk). Each history state can take up the full size of the image. Several hundred GB is not uncommon, and personally I would never work with less than 500GB - 1TB available scratch space.