I was thinking from the usability point of view. I thought that if I configured something in advanced mode and switched back to general that would overwrite my advanced settings.
On Asus RT-AC68U
Firmware Version: 384.8_2
On VPN Server - OpenVPN page
Client will use VPN to access [LAN only, Internet only, Both] setting is not available if VPN Details is set to Advanced Settings
It is still possible to set this setting in General mode then switch to Advanced Settings and...