I'm trying to think of what means SIE and Apple would benefit from a gaming alliance. Mobile is a very obvious area: SIE could leverage iOS and Apple Arcade for mobile spinoffs of popular & legacy IP, a lot perhaps potentially exclusive to iOS & Apple Arcade in the mobile space, or providing iOS/Apple Arcade members free perks (and/or additional perks if they also have PS+). Perhaps some merged Apple Arcade & PS+ package for mobile and console owners.
Beyond that I'm guessing there would be benefits for PS Studios getting live-action film & TV productions for certain games, and Apple getting content perks for Apple+. IF Apple have any ambitions of doing serious game development in the AA and/or AAA space, partnering with SIE could give them a wealth of talent, expertise, and resources to work with and together they could forge ahead with new IP.
It gets more curious when looking at other areas, though. Now, Apple are always the first up for TSMC's most advanced node processes, and that probably also gets them favorable pricing due to volume of orders. A partnership with SIE where Apple absorbs costs for system manufacture in exchange for handling distribution in, say, America and Europe, might not actually be so bad an arrangement. It doesn't mean SIE suddenly are using Apple silicon in PS systems, or switch to Intel: they'd still get AMD and still use x86-64 (and maybe ARM depending on what AMD has). But with this type of arrangement, I guess SIE & AMD would design the chip, then SIE puts in the orders with Apple through to TSMC. The two decide splits, with Sony paying for what systems they'll distribute and Apple paying for what systems they'll distribute. Then the two go to assembling their respective stock and selling them in the territories they'll handle.
I think an arrangement like that could actually work for all parties involved. Of course there's still matter of who gets the cuts from B2P & MTX sales, but I think that could be handled pretty well. For 3P, I think in any markets where Apple PlayStation (man it is weird typing that) are sold, Apple & SIE should split cuts on B2P & MTX sales, but in territories where Sony PlayStations are sold, SIE keeps the 30% cut or at least retains majority cut. To balance that out, Apple port some of their apps to PlayStation with access tied to PS+ subscriptions, and Apple get a small portion from the sub tiers with that content plus get to retain 100% MTX revenue.
Meanwhile SIE & Apple integrate some PS+ & PSN features into Apple Arcade and Apple+ so Apple users can cloud stream PS games (if they have PS+ they can stream those through Apple Arcade or Apple+). Meanwhile maybe take a generation gently porting SIE games to macOS and/or iOS (in a much more sensible way vs. what they've currently been doing, i.e don't port big traditional AAA 1P games until maybe 2-3 years to macOS, 4-6 years to Windows (and in many cases, just don't port to Windows at all while having longer gaps for macOS ports depending on the title), 4-6 years or later to iOS), help cultivate 3P game presence to macOS along the way. Then post-PS6 basically switch to Apple silicon, macOS & iOS fully for future dedicated gaming hardware SIE/Sony and/or Apple may choose to make as desired (such as PS7).
If they want it to be a partnership that's really synergized up & down the pipeline, I think something like this could be feasible. But, depends how true any of this rumor even is :/