Allow only LAN access for WiFi and route rest via mobile data

I have a rooted device, and I want to use the internet via mobile data and let the LAN access via WiFi, but when the WiFi is connected, the gateway changes to WiFi. I have read similar answers like this which uses iptables, but I couldn’t get it working — likely due to my limited experience with iptables. Some suggested using AFWall+ and NetGuard, but that too didn't work. Now, I have managed to set up IPv4 access (i.e., I could access any IPv4 sites), and local access is also set, but only IPv6 is a problem now. I could ping IPv6 addresses, but for example, if I visit facebook.com, it wouldn't work. While modifying the hosts file to 2a03:2880:f184:186:face:b00c:0:25de www.facebook.com works, I need it to be done automatically by the default DNS server Would really appreciate it if someone could help me with it.