Taken from this [suggestion][1], go to
https://takeout.google.com/ and click the "Deselect all" hyperlink, scrolling to the end of the page to check "YouTube and YouTube Music."<br><br>
[![Youtube Content Options][2]][2]<br><br>
With the "Multiple formats" button below, premium users may get an alternative to `csv` in their output. just to the right of it there is an "All youtube data included" button. Click it, (see graphic) again click "Deselect all" at the top, select *playlists* below, and click the ok button.
Optionally check *[music-library-songs][3]*, as that file contains the full url and the video description, which the playlist does not have.
Click "Next Step" below, and, then if the defaults seem reasonable, click "Export".<br><br>
The export duration should be short, after which a username/password prompt is provided for file access. Navigate to the Downloads location for the `takeout-yyyymmddid_number-001.zip` and navigate the the folders in the zipped archive *\Takeout\YouTube and YouTube Music\playlists* to `Liked videos.csv`, and also, optionally, to the `music-library-songs.csv` in the adjacent directory.<br><br>
The *music-library-songs* appears to be a more recent addition in the personal collection, thus the liked videos only go back 2-3 years or so. This is an instantly searchable list, whereas older video ids in the *playlist* must be ported to a search script where they will be url encoded for web verification.


  [1]: https://webapps.stackexchange.com/a/143079/171892
  [2]: https://i.sstatic.net/Oojxj.jpg
  [3]: https://music.youtube.com/library/songs