In a graphical emacs -Q instance, open any Org file. Export it as PDF and open (C-e l o). Then do the same again. Emacs prompts "File foo.pdf changed on disk. Reread from disk (yes or no)" although no external program (not counting latex as external here as it was started by Emacs) actually changed the file.
Emacs : GNU Emacs 26.3 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.14) of 2020-03-26, modified by Debian Package: Org mode version 9.4 (release_9.4-103-gf0b8de @ /home/erik/.emacs.d/straight/build/org/)
