You cannot monetized them. All the ad revenues go to the music owners automatically. RU-vid have an inhouse "Content ID" system, that works most of the time. Sometimes, it incorrectly attribute the revenue to the wrong owner. But something like Adele, or quite well known, will be correct. You don't get copyright claims because these videos just makes more money for the music owners. People who makes these mostly do it for fun. Some send people to their patreon or merch, that's about it. If something is easy to do to make money, it will be oversaturated. If it isn't already, it will inevitably be. Good info to remember.
