- Open the application called ‘Terminal’
- In this application run the command:
sudo eos-fix-ostree-repo && flatpak update
https://support.endlessm.com/hc/en-us/articles/208248596-Does-your-computer-support-Flash-Adobe-Flash-
How to Install Adobe Flash Player on Endless OS Tutorial: https://community.endlessos.com/t/how-to-install-adobe-flash-player-on-endless-os/7559