gimp 2.10.20 hold closed file open
GIMP 2.10.20 flatpak as well ass from package 2.10.20 from ubuntu repo
LM20 5.4.0-42-generic KDE Plasma 5
after closing the last open file this file stays open hold by gimp until closing gimp too or open the next file
unmounting external devices like pendrive give then the erro can not unmount there are open files or so
this is an old issue
reproduction is easy, just following the steps open a file do something with it save it close it and look it is still open
as in the attached file you can see it is hold already for over five minutes and it stays open until gimp get closed