is not a bug in the x2go client.
The same is in the KDE file manager Dolphin (version 20.08.3)
when connecting via SFTP.
the "port" is not commented out in /etc/ssh/ssh_config, then
Dolphin connects to the port specified in /etc/ssh/ssh_config,
and not the one specified in the address bar.
comment the "port" in /etc/ssh/ssh_config, then both the x2go
client and Dolphin begin to connect using the ports specified