The partnership between Sony and Square seems to be collapsing?
No, it's just your wishes.
They just released the little exclusive Final Fantasy VII Rebirth a few months ago plus there's minimum the 3rd FFVII remake chapter coming. They have other exclusives like FFVII Remake, FFXIV, FFXVI, Valkyrie Elysium and the big new IPs they released this gen (Babylon's Fall, Forspoken and Foamstars, even if weren't big successes) plus many games that are on PS4/PS5 and Switch but not in Xbox. Some of these exclusives may be timed, when published elsewhere will mean that their timed exclusivity ended, not that their deal is collapsing.
They have over 150 cameo bots in the game with several dozen different IPs from Sony, Capcom, Activision, Bandai Namco, Sega, Konami, Koei Tecmo, Arc System Works, Oddworld Inhabitants, Mediatonic/Epic, Ember Lab, BlueTwelve, Polyarc, and maybe more.
The legal work to get all of them must have been a nightmare and a lot of work and money. And well, they had to save some popular ones for DLCs or sequels from these comanies and also others like EA, Take 2, SE, Ubisoft, THQ or Devolver (just to name a few) for DLCs or sequels.
There's even also many iconic Sony IPs that aren't in the game, if they decided to don't put it here and place 3rd party or minor IPs instead must be because they plan to add them later, post launch/in DLCs or in a sequel.
And well, before this game there were already SE cameos in Astro's Playroom.