Nice hint. Unfortunately the referenced bug report does not tell what the faulty .conf looked like, but an attached log tells “host not found: localhost” when postfix refused to work…
Maybe looking also at /etc/resolv.conf when things don’t work might be useful.
Here too nsswitch.conf is unmodified, resolv.conf acts as expected (changing according to the connected interface as configured) and everything OK apparently, even after the glibc-2.33 and kernel 5.10.16 update.