The display resolutions are listed in SystemInformation[]. You can use the short form SystemInformation["Devices", "ScreenInformation"] as well.
12.1.0 - 12.3.1 has an active compatibility shim which forces 96dpi displays to report as if they were 72dpi. Evaluating the following will disable it, but I would restart the FrontEnd afterwards.
CurrentValue[$FrontEnd, "ScreenResolutionCompatibilityMode"] = False
With that said, there is no direct equivalent to the old mechanism. i.e., you cannot alter the resolution just for the fonts.
