From NiclasZeising 20200223:

Having a big configuration file in /etc/X11/xorg.conf is the old way of configuring xorg;, it is, to my knowledge still supported. Having config snippets in /usr/local/etc/X11/xorg.conf.d/ is the new way, then you can add config snippets there, either as a sysadmin, using a configuration tool or if your package depends on it, if you are a package maintainer.