For some reason Calibre won’t let me do anything because “drive is full” which I assume has to do with this.
Update: I believe I “fixed” the error with Calibre by using FlatSeal to add environment variable CALIBRE_TEMP_DIR that changes the Temp directory to something else. So far that’s the only program I’ve seen give trouble.
Fyi if you find it annoying to see this this everytime you open Dolphin, you can right-click it and set it to hidden