@deflektor said in retroarch GUI can't "save config on exit.":
people are still likely reading this thread because of Google - and walking away without a solution.
(1) Disable 'save on exit'
(2) Replace the contents of /opt/retropie/configs/all/retropie.cfg with the contents of /opt/retropie/configs/all/retropie.cfg.rp-dist and the contents of every system-level RetroArch config file at /opt/retropie/configs/system-name/retropie.cfg with /opt/retropie/configs/same-system-name/retropie.cfg.rp-dist.
This will leave the user with default RetroArch settings, but it's the only way to advise everyone at once without knowing the extent of an individual's problems.