How do I disable IPv4 and enable IPv6 in Linux?

Disable IPv4 on Boot

On Ubuntu 18.04, you need to edit /etc/netplan/50-cloud-init. yaml . If you enabled IPv6 when the Droplet was created, remove the IPv4 address and gateway4 lines. If you enabled IPv6 after creation, you need to add the IPv6 address and gateway6 lines.

Should I disable IPv6 Linux?

If you are not using IPv6, or at least knowingly using IPv6, then you should turn off IPv6 and only enable it again when you need to deploy services on IPv6. If you have IPv6 enabled but you are not using it, the security focus is never on IPv6 or vulnerablities associated with it.