This is a well-known bug that the installation script has been carrying around for well over a year. I don’t know why it hasn’t been fixed yet.
The problem: The installation script has apparently not initialised the database and has not created the files. This is why the daemon crashes (the return value 255 originates from the crashing script under bin/daemon.php
My workaround:
Access the server via SSH
Switch to the Friendica environment with sudo yunohost app shell friendica
bin/console dbstructure update creates the database structure
Unfortunately, the user specified in the YunoHost installation is not available in the DB, which is why this user is also created on the console:
bin/console user add <username> <nickname> <mail-address> <language-code> where the mail address must be the one selected for the admin at YunoHost
Set password with bin/console user password <password>
You can then log in to the web as this user and have admin rights.
So I poked around some more and it’s POST_INSTALL.md that’s wrong.
You can log in with your normal YNH user (not user@domain.tld as docs claim), the first attempt will fail for some reason, but the second attempt will just bring you to the timeline.