Yes, we are aware of the issue. The app-center has started crashing because a flatpak bundle is installed on your system. We are in-process to resolve the issue but it will only be available on the next EndlessOS update.
For now, I would recommend you to uninstall the flatpak bundle (com.github.nomacs) in your case.
- Open Terminal
- Type
flatpak uninstall -y com.github.nomacs
Probably restart and see if the app-center opens up. Let us know.
Thanks