Yeah, IPv4 will indeed be behind CG-NAT on those 4G connections, so no port forwarding. But if you have IPv6 (and Vodafone haven’t firewalled the ports) you can try that - at the moment IPv6 in Plex is a manual setup though: Ipv6 support for myplex - #269 by thornrag
Alternative is using a VPN - either a peer-to-peer one like Zerotier/Tailscale (which requires a client to run on both server and clients), or a centralized one where both the client and server connect to a central VPN server.
