Unable to log into alternative unprivileged user with default GNOME shell on Edubuntu 24.04 — sudoer (uid=1000) works

I just installed Edubuntu 24.04 for my daughter and because I knew that the user created during installation is an admin, I opted to create her user account from the Settings application after installation.

I am able to log on with the "primary" user (created during installation) without an issue. But any attempt to log in with her user lands me back on the login screen, despite the password being correct (I know, because a wrong password gives a different and visible error).

A handful of modifications were done during installation or immediately afterward:

When logon failed, my initial hunch was to flatten the $HOME for my daughter's account. So I did that with xdg-user-dirs-update --force after changing into her user context on the terminal.

That didn't help. So I removed the account and user directory and then re-created the user account.

That also didn't help.

I am at a loss regarding what is going on and how to fix it by now. I picked Edubuntu for it was touted as suitable for children, but otherwise I don't use Ubuntu or GNOME anymore for my daily work. Not even sure this question is specific to Edubuntu at all.

How can I diagnose and fix this?

Output from journalctl --follow while attempting the logon interactively. The username was replaced by daughter and hostname as well as timestamp was stripped for brevity.

For good measure:

$HOME/.config/user-dirs.dirs:

and $HOME/.config/user-dirs.locale:

In the context of my user's account (but from a terminal):

(seemingly from /etc/profile.d/edubuntu.sh)

but for my normal user:

(seemingly from /etc/X11/Xsession.d/55gnome-session_gnomerc)

Edit 20:52Z:

I tried it again with systemd-coredump enabled and looked at the strings of the resulting coredump which yielded:

For the /usr/libexec/gnome-session-binary running greeter the value was (retrieved from /proc/.../environ):

For my own user it was:

As can be seen from my edits and as was suggested by the comment of steeldriver what is wrong is the value of XDG_DATA_DIRS.

My workaround (not a fix and no diagnosis beyond the comment and my question) was to populate ~daughter/.pam_environment with the line:

... retrieved via the user for which it works.

PS: I will happily accept any actual fix with steps to diagnose instead of this.