Found on different forume
So, I finally found the solution to this.
Apparently, only Lan port 4 of the router Nokia G-140W-C can do bridging mode. All the other ports can't.
I have done the change and it's working for me now. Finally, I can use my Asus router for everything, and Nokia router just for termination.
Please try, I am sure it should work for everyone.
The changes you need to do on the Nokia router are just 2:
1. Change the Lan port 4 to bridge mode (it will need a restart)
2. Enable IPoe mode in WAN settings. (Just restart after this to be on the safe side, though it doesn't need a restart)
Happy bridging and please don't forget to upvote if it works for you