Each platform you link to your Epic Games Account shares its inventory with your other connected platforms. There are a few exceptions.

Shared Across Platforms

• All earned free drops (Common Items, Event Items)
• Season Rewards & Titles
• Rocket Pass Items
• Item Shop Purchases
• Blueprints and items built from Blueprints
• All Rocket League-branded DLC included in the Legacy Pack
• Esports Shop Purchases
• Fan Rewards 
• RLCS Attendee items 

Not Shared

• Platform-Exclusive Items: e.g., Sweet Tooth, Hogsticker, Armadillo, Mario and Luigi NSR, and Samus' Gunship
• Ultimate Edition On-Disc DLC: Batman/DC Superheroes Pack
• Premium DLC Packs: licensed content that was previously available in the Showroom (e.g., Back To The Future, Jurassic World, DC Superheroes, Fast and the Furious, Ghostbusters, Knight Rider, etc.)
• Purchased Credits and Esports tokens balances