Hi Marius and Guix,
> To make the glibc 2.28 locales available and get rid of this warning for
> packages you haven't updated yet, add this to your configuration and
> (locale-libcs (list glibc-2.28 (canonical-package glibc)))
That did the trick, thank you.
I added urandom-seed to the services for this system, but reconfigure failed because I use the desktop-services as a base, which includes urandom-seed as a service from base-services.
The reconfigure and reboot did not hang this time, though.
Everything else I use looks good, thanks!