ufw was not installed by default. Something else was installed that I had to uninstall cause it also didnt work.
Proxy is danted SOCKS5 proxy server on rpi3.
Port 6881 is open in the router on the side of rpi3 and in ufw of rpi3. Rpi3 reports tailnet IP to be listening on port 6881. Port checker says that port 6881 is closed.