Everything for now, Multiplatform as in PS5 and PC in the future.
This is from Bungie's faq on the topic:
Q. Bungie has future games in development, will they now become PlayStation exclusives?
No. We want the worlds we are creating to extend to anywhere people play games. We will continue to be self-published, creatively independent, and we will continue to drive one, unified Bungie community.
The fact that they're being so forward about it, is a fairly good indication that it won't be leaving the Xbox platform.