It's difficult to fathom why this change was made in Ventura. It certainly makes life much harder for those of us that rely on the feature, and I doubt anybody who doesn't would find the network settings any easier to understand.
The good news is that the feature still works as before, and if you have any locations other than the default "Automatic" location then there will be the usual "Location" submenu in the apple menu at the top-left of the screen. You can quickly switch locations using that, and then configure the current location's settings using the System Settings app.
What you can't do via the GUI any more is administer locations, as you rightly describe. To do so you have to resort to the command line, specifically the "networksetup" command.
The location-related options for the networksetup command are as follows:
Usage: networksetup -getcurrentlocation
Display the name of the current location.
Usage: networksetup -listlocations
List all of the locations.
Usage: networksetup -createlocation <location name> [populate]
Create a new network location with the spcified name.
If the optional term "populate" is included, the location will be populated with the
default services.
Usage: networksetup -deletelocation <location name>
Delete the location.
Usage: networksetup -switchtolocation <location name>
Make the specified location the current location.
So if you wanted to, for example, create a new location "Test" and populate it with the default services for your machine, you would enter the following in Terminal:
networksetup -createlocation Test populate
Once you have added a custom location the "Locations" submenu will appear in the apple menu (and will be absent otherwise). Hope this helps.