Once you have connected your YouTube Music account to Soundiiz; we are able to retrieve your playlists, liked songs and artists (not your saved "Albums" or library "Tracks").
However; be aware as we are using the YouTube API (while there's no Google dedicated API to YouTube "Music"), we are only able to retrieve artists subscriptions you have made with your YouTube account.
Your YouTube and YouTube Music account should share the same artists subscriptions as long you are using the same "channel". Be sure to use the same "channel" on both YouTube and YouTube Music app and connect this specific channel to Soundiiz.