i went to:
https://y2mate.com/
and put in a utube song and picked the audio tab, and the m4a option. it opened into the browser and started playing as audio only in the browser, but i clicked the 3 button icon and was able to download as videoplayback.m4a
it did NOT play in my winamp.
it DID play in my VLC.
mp3tag shows no tags and says its a mpeg-4 AAC.
mediainfo says its a AAC LC.
i picked the mp3 option, and that file PLAYED in winamp.
my guess is there is something wrong with the m4a container or file header y2mate creates, that winamp rejects, but that VLC forgives. however, i suppose it is possible winamp has a bigger problem with AAC LC in m4a container files, but i think more people would be posting such if true.