Hetzner has some docs: https://docs.hetzner.com/robot/dedicated-server/ip/additiona...

Since I only needed about 3 VMs (though each being a bit beefier, running containers on them, a web server sitting in front of those with vhosts as ingress), I could give each VM its own IPv4 address and it didn’t end up being too expensive for my use case. Would be a bit different for someone who wants many small VMs.