Hardware A: Ubuntu 20.04 (192.168.1.61):
Installed VNC server and added OpenVPN client config to some remote server C.

Hardware B: MacOS 11.1 (192.168.1.51): standart preinstalled VNC client.

From B to A i have perfect VNC connections when OpenVPN is disconnected. But when connect from A (as client) to OpenVPN server, VNC connection is immediately down. At the same time smb, ping (A <-> B) and traceroute (A <-> B) works perfect and with same behaviour like with disconnected OpenVPN (down only VNC).

From B to A (with and without VPN):

% traceroute 192.168.1.61

traceroute to 192.168.1.61 (192.168.1.61), 64 hops max, 52 byte packets

 1  192.168.1.61 (192.168.1.61)  27.855 ms  2.296 ms  35.563 ms

From A to B (with and without VPN):

$ traceroute 192.168.1.51

traceroute to 192.168.1.51 (192.168.1.51), 64 hops max, 52 byte packets

 1  192.168.1.51 (192.168.1.51)  27.855 ms  2.296 ms  35.563 ms

Why VNC isn't work when OpenVPN client connected on VNC server and how to bypass this behaviour? I need connect VNC server to OpenVPN network and don't lost VNC connection in same time.