If someone uploads a video in h264 1080p, then the video is transcoded to h264 (at a lower bitrate) and to vp9. But if some time later, the video gets many views then the video is transcoded to AV1. So, the file with the highest quality would be the one in VP9, since I don't think YouTube keeps the original file until the video gets popularity.
Is this true? Will the video with the best quality always be the one transcoded to VP9?