This is a guide on how to install Tailscale within an LXC which is already behind a physical router such as PfSense.
Operating System: Proxmox VE 6.4.x
Container (LXC) Host Operating System: Ubuntu 18.04 Standard
Topology: Internet > WAN > PfSense > LAN > Proxmox > Tailscale LXC
Firewall/Router: No modifications required