Charter has been quietly rolling out MAP-T. It's a little different than CGNAT but still involves multiple customers sharing an IPv4 address. However the customers are sharing a standard public address not sharing in the 100.x.x.x range. https://pc.nanog.org/static/published/meetings/NANOG71/1452/20171004_Gottlieb_Mapping_Of_Address_v1.pdf
You will see other ISPs worldwide rolling out CGNAT or MAP-T as well. They are all out of IPv4 addresses or close.
As you say you can do VPN based port forwarding. Wireguard / Tailscale work fine behind MAP-T. Or, just use standard IPv6.
Ubiquiti AirMax