Can DSC be used to capture settings of an already existing device?

I’m curious to know if you already have a pre-existing device (domain controller, file server, etc.) already configured if DSC can be used to capture those settings in a configuration file that you can use to apply to other servers. Thanks in advance for your input.

Nope, DSC doesn’t do that. There is a third-party tool out there called GuardRail (from ScriptRock) which will inventory a Windows system, and supposedly can even generate a DSC configuration from that, but I don’t have much personal experience with it yet.