That is the universe telling you that you shouldn't be using port forwarding lol.
What is the IP address of your BI computer and what is the IP address you typed in for port 81 in the router?
Post screenshots and it usually will show the problem was a transposed number.
And who is your ISP? Some provide a system that port forwarding won't work due to the nature of how IPs are assigned.
But like use Tailscale or Wireguard for safer remote viewing.