Hi there, I'm having the exact same issue. Is there a version of the Cloudron installer that actually works? Kind of a discouraging sign to see these types of issues when following the official instructions.
An IPv6 issue was called out on Reddit 2 years ago related to Ubuntu 20.04 server. Is this the problem? https://www.reddit.com/r/ipv6/comments/lq7clv/ubuntu_2004_will_not_pull_dhcpv6/
If Cloudron does not support installing on local machines at home machines, please let me know so I can look for alternatives.