UniFi doesn't use VyOS anywhere afaik. Some Ubiquiti products run EdgeOS which is a Vyatta fork (EdgeRouter, the original security gateways). More recent UniFi products (UDM, UDM-SE, UNVR, etc) run UniFi OS which is their own Debian-based OS that runs applications inside Podman containers.
It is not very elegant though.
Do you know of an open source router that does what you are looking for?