What if my home computer has a public IP address (which it does, since I use IPv6 only)? It's not always so simple. There's also the option of my phone connect

What if my home computer has a public IP address (which it does, since I use IPv6 only)? It's not always so simple. There's also the option of my phone connecting to my home pc while it uses 4G (while the PC uses the land connection).