I was about to write the same comment but you expressed it much better. I would also be happy if it could be both an android tablet but have a monitor mode where it just becomes a monitor.
You can host a relay inside of a Docker container if you need it as well and it even supports AV1. There's also password auth for each device and permission control.
They have a mobile app too, though I haven't used it as much as the desktop variety, might be worth a shot.