Supporter's TV on virtual machine behind NAT
For Desktop TV app to act as supporting party in remote assistance session and installed / operating from within virtual machine, latter one behind NAT (guest to host operating system) any ports for inbound traffic must be open or forwarded? Of course there is one more NAT on supporter's side: LAN to Internet router built-in NAT.
Supporting TV app runs in Ubuntu 20.04 v.m. powered by VirtualBox. Both of latest available stable releases. It supports others through Internet. Supported party is Android 10 smartphone with TV QS app current version.
I raise this question because for setup as described above establishing remote assistance session does't succeed. However, what succeeds is to support same remote party from iOS TeamViewer app which operates in same LAN as mentioned Ubuntu TV on Ubuntu 20.04 in v.m. setup.
Any other technical points than ports to be open are to be examined during troubleshooting?