Cross-platform is not officially supportend by EA/Maxis.
Sims 4 has been release on several platforms and game shops and many have questions about how they are compatible among each other and what has to be bought anew.
The base game itself is now free everywhere which leaves the question of the DLC. It can be attractive to mix-and-match since different shops have different sales.
The FAQ below gives an overview on what you can combine and what not.