The comment I linked you to fixes this. No “try” about it.
Applied the fix referenced in the provided link via SSH. I then restarted Webmin via SSH. The create button is now visible in create virtual server config and the network interface error is gone. I then rebooted the instance via SSH, but now cannot connect anymore via SSH (I gave it 10 minutes - no dice). Also rebooted the instance completely and still no SSH.
It seems that the proposed solution breaks network connectivity somehow on AWS LightSail Debian 10. I will now have to perform another snapshot migration to a new instance and do it all over again without apply the 2.011 update.
I think there are still some issues to work out here! 