VCN address for screen share

You can also use hostname.local entry instead of the vnc:// URI, where the hostname component is the actual host name of the Mac whose screen you are receiving. This name can also be seen in the Finder's sidebar under the Network category.

IP addresses of computers usually end up changing over time. Verify the currently correct IP address for the computer you want to connect. @VikingOSX's suggestion to use a DNS name with ".local" is a good one which eliminates the need for worrying about changing IP addresses, but this only works if both computers are on the same subnet (usually the case with simple home networks).

I only have Screen Sharing experience where both Macs are on the same LAN segment in my home.

Entering hostname.local on the receiving Mac won't buy you anything because the source Mac is not on your subnet or even physical location. I expect two things would need to happen: 1) proper network masking and/or opening the firewall in front of both Macs to pass the VNC port 5900 packets. The Network Administrator may resist doing that.

Have you checked the firewall in front of both Macs to ensure that it is allowing port 5900 transmissions to get through? Did anyone change the premise firewalls at either location? Otherwise, I can be of no further help with this remote VNC session.

I'm afraid the main point(s) are being lost. For over a year I used "*k" to bring up the window where I put in "vnc://c-73-38-192-144.HSD1.ct.comcast.net/" and I could start screen sharing with her credentials.

Someone configured your router to port forward the VNC port to your Mac. That hole you poked in your router appears to have been closed, or Comcast changed the hostname of your external IP address. Since that address is from a Comcast domain, it is the external address Comcast assigned to your Modem. They may have changed that hostname.

You could use WhatsMyIp on the destination Mac to determine the external IP address and try to VNC using that. If it works, then your hostname has changed. If it doesn't work, then the hole you poked in your router/firewall is now closed.

And, now if anybody can figure out your new hostname or external IP address from the previous one you posted, they know you have an open hole in your router from which they can run VNC exploits to attempt to take over your Mac.

Comcast is good at randomly assigning external IP addresses from anywhere. I am in the midwest, and for a painful amount of time, Comcast gave me a different network number from New Jersey which really jacked two-factor authentication maps, and as you have pointed out, any hardcoded addresses.

You should never post any personally identifiable information online which includes the IP address assigned by an ISP.

You should use a Dynamic DNS Name provider for the remote location so you can access the remote network using a DNS Name that does not change since the Dynamic DNS provider will monitor the IP address and will update the IP address when the ISP changes it. So all you need to do us use the DNS name to access the remote network. There are multiple providers of this service available.

I've never investigated the lower level details with macOS screen sharing, but I do know VNC connections are absurdly unsecure so you should only be running a VNC connection through an encrypted SSH tunnel. Doing this also hides the VNC port from the outside and only leaves the SSH port exposed. By default macOS does not enable SSH by default (I believe macOS calls it "Remote Management" in the Sharing System Preferences). It can be tricky at first on how to route the VNC connection through an SSH tunnel since so many "guides" online don't really explain the process and end up using identical ports for both directions making it harder to understand.

Why do you think that address is invalid? It looks like a very valid Private Class A IP address.