Re: invalid value for parameter "default_text_search_config": "public.pg"

> I'm not sure what applied="public.pg", error="setting could not be applied"
> means.

No, "applied" is "f" (false), meaning that the setting is not actually usable.
I'm a little surprised that it seems to have gotten into your live session
anyway, although perhaps that's because the postmaster can't really
validate it at startup.

> I can change it in the config file, no problem. I just would like to
> know if this is a simple configuration error, or a software installation
> error. (Is public.pg a built-in config that should always exist?)

"public.pg" is certainly not a standard (as in built-in) text search
configuration name.  Maybe that value was installed by some bit of
software that failed to install the configuration to go with it,
or only put the configuration into one database not everywhere in
your installation?