YouTube Music doesnt have an official desktop app just yet, you can only access YouTube Music from your PC or Mac by navigating to the desktop site. The YouTube Music online site doesnt have download feature for YouTube Premium and YouTube Music Premium users. Given that many people need to download YouTube Music to computer for offline playback, Ondesoft has developed a YouTube Music desktop converter, which makes it fast and easy to download and convert YouTube Music to MP3, M4A, AAC, FLAC, WAV, AIFF losslessly at up to 10X faster speed.

https://www.ondesoft.com/youtube-music-converter-for-windows/