GRE. IPIP. The young people with their cloud nonsense. They do not understand the beauty of simplicity.
Back in the days before WireGuard existed. Before the cloud nonsense took over. We ran production GRE tunnels between three continents without a single kernel module beyond the basics. No crypto overhead. No handshake dances. Just packets in packets. The routing table was the documentation.
The young people will defend their WireGuard. Their OpenVPN. Their IPSec nightmares with redundant feeds and certificate management. But when you need to tunnel a multicast stream across two ASNs without touching userland. GRE is still there. Waiting. Patient.
IPIP for IPv6 inside IPv4. That is all I will say...