Sorry for a little be off topic query.

I am checking which VPN solutions are IPv6 compatible outside and inside the tunnel and can so transport with any IPv6/IPv4 connection IPv6/IPv4  internal to then tunnel  

Maybe somebody made such tests already and can point me to it.
What i found so far:

Citrix SSL VPN ( seems to have only partial support)
https://support.citrix.com/article/CTX211780 NetScaler Gateway VPN users are not able to resolve IPv4 DNS when their ISP has IPv6 enabled.  

OpenVPN

Wireguard (LINUX only)
seems  to support it but missing other stuff like hostchecker