You can’t move “var” to a “System files” folder. This would break programs which expect /var to be, well, at /var. Long ago on macOS, everything was in “System

You can’t move “var” to a “System files” folder. This would break programs which expect /var to be, well, at /var. Long ago on macOS, everything was in “System Folder”, and it worked fine, but macOS has since inherited a massive Unix legacy. Thumbnail caches are not stored on USB drives, they’re stored somewhere else, away from your files.