Once a Season Pass has been applied to your save data, it will carry over with Cross-Save. If you already have Cross-Save enabled, then regardless of the platform you play on and purchase on when using your save data, the Season Passes will apply to your active Save Data. So, if you normally play on Playstation, and you already have Cross-Save enabled with your Xbox characters as your primary save data, when you purchase the Deluxe on Playstation, it will apply to your Xbox save data. To put it simply, if you purchase the Deluxe on the Playstation, the Season Pass unlocks will apply to the first save data you log in with, which, in your specific case, will be your Xbox save data. You don't have to purchase it on Xbox first. If you're moving to Playstation forevermore, you can simply purchase stuff on the Playstation and not worry about making any purchases on the Xbox for Destiny 2 into the forseeable future. Just make sure you never disable Cross-Save. If you don't already have Cross-Save enabled, make sure and do that before you make the purchase and log in. (I add this extra clarification in case someone else views your question.)