Add songs to Library when adding to playlist - greyed out
The reason your Add songs to Library when adding to playlists checkbox is greyed out is because you haven't enabled the iCloud Music Library (see the checkbox above the one that is greyed out).

If you enable iCloud Music Library, then you can store your Apple Music songs and playlists in iCloud and access them across all your devices.

In summary, by ticking the iCloud Music Library checkbox, the Add songs to Library when adding to playlists checkbox will no longer be greyed out. Then you can enable/disable it as you wish.