NBC on FireStick
The NBC network has a variety of channels for every genre, so I’m not surprised you are looking for a way to watch it on Firestick. My advice is to follow this guide https://www.firesticktricks.com/nbc-on-firestick.html You will easily install the NBC app on your Fire TV device and will be able to enjoy your favorite content again.
NBC is free if you are getting it off the air. Getting it on IP-based networks equates to retransmission of the broadcast signal, which is what cable companies actually do, and pay NBC corporate for the privilege of doing that. Those cable companies, need to recoup their costs if you decide to use another retransmitting provider over IP based network. Simple as that. You have to pay the piper. Which piper doesn’t matter. Or get your broadcast signal with rabbit ear antennas for free and don’t complain about the signal strength.