I started testing out elementary OS 6 on a couple of devices, and there seems to be a problem restoring the default Web Browser back to Web (Epiphany). After installing Firefox v91 from Flathub and using System Settings > Applications > Default
tab to switch it to the default browser, the original entry for Web has disappeared.
I tried the suggestion from this discussion to use the xdg-settings command to reset it, but I cannot even find the .desktop files for the program in either /usr/share/applications
or ~/.local/share/flatpak/exports/share/applications/
.