@Derelict I think i got it to work. After i set the default gateway manually to the VPN and not automatic and saw that it worked,
i transfered the Flowing Rule i made for the outbound traffic to the Lan interface.
With the new knowledge of your help and the help of viragomann i changed some tiny things in the firewall rule.
After that i changed the default gateway back to automatic and know the outbound traffic takes the vpn and everything works.
I even rebootet the firewall to get lost of the states but everything still functions as it seems.
Thank you so very much for your dedication and your help.