Thanks,
this worked well, however, I got an “ERROR: launchpadlib 1.10.13 requires testresources, which is not installed” (this didn’t stop the installation though) on Ubuntu 20.04 minimal (1 vCPUs| 1 GB RAM 2GB swap| 50 GB disk). And the installation aborted at later stages (not sure if it was because of the RAM but was not able to capture the error). I re entered the installation command after installing testresources (here). And manage to complete the setup without error and managed to get ERPNext 13 running.
Suggestion: Please also add that the ports have to be opened in ubuntu firewall. It took me sometime to figure out why my installation is not working.