YouTube Mix playlists have 0 video ids

[maxsupermanhd]

Checklist

• I'm reporting a broken site support issue
• I've verified that I'm running youtube-dl version 2020.09.20
• I've checked that all provided URLs are alive and playable in a browser
• I've checked that all URLs and arguments with special characters are properly quoted or escaped
• I've searched the bugtracker for similar bug reports including closed ones
• I've read bugs section in FAQ

Verbose log

$ youtube-dl "https://www.youtube.com/watch?v=QlhopscNIw4&list=RDMMQlhopscNIw4&start_radio=1" -v
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: [u'https://www.youtube.com/watch?v=QlhopscNIw4&list=RDMMQlhopscNIw4&start_radio=1', u'-v']
[debug] Encodings: locale UTF-8, fs UTF-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2020.09.20
[debug] Python version 2.7.17 (CPython) - Linux-5.7.0-050700-generic-x86_64-with-Ubuntu-18.04-bionic
[debug] exe versions: ffmpeg 4.2.1-0york0, ffprobe 4.2.1-0york0, phantomjs 5, rtmpdump 2.4
[debug] Proxy map: {}
[youtube:playlist] Downloading playlist RDMMQlhopscNIw4 - add --no-playlist to just download video QlhopscNIw4
[youtube:playlist] RDMMQlhopscNIw4: Downloading page 1 of Youtube mix
[download] Downloading playlist: RDMMQlhopscNIw4
[youtube:playlist] playlist RDMMQlhopscNIw4: Collected 0 video ids (downloading 0 of them)
[download] Finished downloading playlist: RDMMQlhopscNIw4

Description

It looks like youtube-dl can not fetch a playlist that is generated by youtube algorithm on-the-fly (radio playlists). Same issue here: #23087
BUT! I would not open this issue if what you commented down for other issue was working for me.
Link "https://www.youtube.com/watch?v=btGjFzQ5_-A&list=RDbtGjFzQ5_-A&start_radio=1" is not working too and failing with 0 collected ids.
I tried adding up my account to this but still (even with auth) it is reporting 0 ids.