AFAIK, if you're a YouTube Premium subscriber (and you select High Quality in the settings) you would be getting a 256kbps AAC compressed audio file versus 128kbps AAC from regular YouTube.
If you then convert it with an audio converter, you could output it to a 24/192 or even 32/384 WAV, AIFF or FLAC file, but you would still have the sound quality of 256kbps AAC compressed audio even though the file size increases proportionally.