Description of problem: The comment in the beginning of /etc/systemd/logind.conf says # should be created by either modifying this file, or by creating "drop-ins" in # the system.conf.d/ subdirectory. The latter is generally recommended. However, the correct subdirectory seems (according to the manual and my own experimentation) to be logind.conf.d.
Looking closer, it seems the analogous problems applies to most if not all /etc/systemd/*.conf files. All of them refer to system.conf.d rather than their respective *.conf.d directories. (The comment is correct in system.conf.) systemd-248-2.fc34.x86_64
We're one step ahead already ;)
FEDORA-2021-775e2373a1 has been submitted as an update to Fedora 34. https://bodhi.fedoraproject.org/updates/FEDORA-2021-775e2373a1
FEDORA-2021-775e2373a1 has been pushed to the Fedora 34 stable repository. If problem still persists, please make note of it in this bug report.
Looks good now. Quick fix! :-)
This was fixed just a few days after the report.