Short answer, yes!
To be clear to others reading this thread - Notion comes bundled with a large number of orchestral and popular instruments on both iOS and desktop versions. Jazz soprano sax however, is an expansion sound in both iOS and desktop versions of Notion. The instrument needs to be purchased on both platforms if you wish to hear it on both. For iOS, the instrument is purchased via Apple's in-app purchase mechanism within the Notion app. For desktop, the instrument sound is purchased from https://shop.presonus.com/
You don't need to purchase the instrument sound to physically write for it however - it will playback with the default piano sound on iOS, and on desktop you can assign any voice to sound when playing back that line instead.