I just want to inform other users that I noticed the problem when trying to install GOS from the browser installed as Flatpak.
The process begins correctly, the bootloader is unlocked, the image is taken correctly, but then the restart process hangs and never ends.
After installing the browser from the Debian/Ubuntu repository and from the .DEB file works properly.
Tested on Chromium and Ungogled-Chromium.
Perhaps it is worth adding a warning to https://grapheneos.org/install/web