add youtube audio track to playlist

Hi, sorry for the lightweight question, but should it be possible to add a YouTube audio track to a playlist? When I try this it pops up with a message saying its been added to the playlist, but when I look it is not there. Adding my own FLAC tracks from USB drive to the playlist is no problem. Should this actually work?

Further to this, if it’s in the queue first then I can save the queue as a playlist ok, but not without the YouTube track being in the queue first. Same applies to web radio. Weird eh?

If you can import local FLAC files, you should probably download youtube videos to flac files and then add them to the the playlist.
To do this, I think tuneskit audio capture is the best choice. It is able to capture youtube to flac without quality loss, and it’s one of the cheapest products of this kind. Plus it is discounted due to their Halloween sale.
Link of the discount coupon: