Yes, it is available in unlocked S10 and it should be available in the S20 as well. The FCC would like all cell phones in the US to have the FM receiver available for emergency reasons: https://www.reuters.com/article/us-usa-fcc-apple/fcc-says-apple-should-activate-iphones-fm-radio-chi...
That requires cell phone signal and a data plan. While I usually have each, there are many places in the mountains where there's no cell phone signal but FM radio works fine. Also, Radio FM app doesn't include all stations.
How do we get it unlocked? Is there a way to tell Samsung to unlock it or petition? My new Tmobile A715G is also no available. Samsung support said US not supported, but this news article says it should be. https://www.sammobile.com/news/samsung-activate-smartphone-fm-chips-us-canada/
I'm using my old Honor 7X to do radio. My old Moto G phones have it too. This is my most expensive phone yet and it doesn't have those basics including voice recording.