The song, that’s free to use for YouTube videos, sounds like a jazz song and it’s in the key B-flat minor (I am a music composition specialist, and by hearing it I knew its key). It begins with a guitar loop. Last time I heard it was in 2021 or so, but I still remember how it sounded like. I think that it wasn’t from YouTube audio library either.
If you know of any specific YouTube videos that use the music you are thinking of, it might be named in that chunk of the video description which automatically identifies music used in the video. Or, failing that, you can ask the video creator.