The docs indicate that you can disable P2P connections by setting --derp-server-stun-addresses \ CODER_DERP_SERVER_STUN_ADDRESSES to empty. This does not work.

      --derp-server-stun-addresses string-array, $CODER_DERP_SERVER_STUN_ADDRESSES (default: stun.l.google.com:19302)
          Addresses for STUN servers to establish P2P connections. Set empty to disable P2P connections.

There does not appear to be any way to set this configuration property to empty:

• Setting the CODER_DERP_SERVER_STUN_ADDRESSES environment variable to empty results in the default value of stun.l.google.com:19302 being used
• Setting the argument --derp-server-stun-addresses="" results in a parsing error: invalid argument "" for "--derp-server-stun-addresses" flag: EOF

Also, there appears to be a bug with parsing string-array environment variables. The value is appended to the default, rather than replaced. For example, CODER_DERP_SERVER_STUN_ADDRESSES="foobar:443" results in the following STUN addresses: [stun.l.google.com:19302, foobar:443]