Do my dad is in his 90’s and living in a senior apartment with my old iMac on High Sierra. He used to have his own Spectrum account, but now uses the facilities WiFi (still Spectrum). I had been trying to use Screens 5 (which I really like) to help him as I had in the past with another screen sharing software, but am unable to connect or even install his end of the software due to a firewall (I assume).
I think I know the answer, but is there some way to connect to his Mac from outside to help him? I tried to have a local friend poke at some ports, but after calling Spectrum, determined that he does not have an internet account, but just has cable and the shared WiFi. I am looking into how much it would be to add internet to his account, or give him a minimal cell phone and HotSpot into his computer. Maybe someone has solved this with a similar situation but I can’t see how to fix it with a simple solution. Obviously they cannot open the WiFi with UPnP as that would make everyone vulnerable. Screens5 mentions Tailscale, but I am not sure what that is or if it would address my problem.