Text Message Forwarding is not showing on iPhone 12 Pro Max running iOS 14 if using eSIM
There appears to be a bug in iOS 14 if you are using an eSIM. The option for Text Message Forwarding will not show unless you put a regular SIM in your phone as well. I just did that and the option popped right up. The regular SIM does not need to be turned on or even active in any way.. I just grabbed an old SIM from my drawer.. but the second I put it in my phone, my phone asked me if I wanted to add another line, I said NO and then went to Settings/Messages and the option to Forward messages reappeared.
It is a confirmed bug I believe as shown in this thread: https://discussions.apple.com/thread/251812933