Thank you @Hank21 - With Omada Controller I was able to add multiple subnets.

Thanks @shberge! IKEv2 is def necessary for multiple subnets. But even after firmware upgrade I was not able to establish connection. But I am working against a Fortigate 1500 D, maybe that's the...

I would like to add a second remote subnet to my running IPsec tunnel (LAN-to-LAN, same WAN interface, same remote gateway). Unfortunately, in the router GUI it doesn't seem to be an option to create...