I'm not sure what you mean by this entirely. Viscosity has the option to block IPv6 traffic while connected under Preferences -> Advanced. If you're looking for something more advanced than this, you will need to script it - https://sparklabs.com/support/kb/articl ... connected/
Those routes are exactly what the previous option I referred to is adding. They should work on both macOS and Windows. If they're not, could you please post some extra information including your route table and information about your connection.
I assume you are referring to to the option below. Is that right? If so, that option only comes into effect if the VPN server does not support IPv6. Is there a way to disable fore the connection if the VPN server does support IPv6?