Connecting through my proxy with psql works just fine, but with the same details in pgAdmin 4 I see this in the logs:
unknown tls handshake failure: 136.41.64.106:60795: tls.RecordHeaderError{Msg:"first record does not look like a TLS handshake", RecordHeader:[5]uint8{0x0, 0x0, 0x0, 0x8, 0x4}, Conn:(*tlsrouter.wrappedConn)(0xc000553180)}
If I'm not mistaken, that's the start of the bespoke handshake.
The sslmode=require and sslnegotiation=direct parameters are set correctly (as well as everything else, matching the PG URL string from working psql.
