Looking at your linked accounts the Playstation is the top one with Steam then Stadia so I've always assumed it's the first one that is the primary account/characters. Let's wait for a forum mentor/ninja to clarify whether that is correct or not but I'm going to say your Playstation account is the primary. If you are planning on any changes to cross save please wait till someone else agrees or corrects me on that. I am cross saved using my Xbox characters so it is showing Xbox then Playstation then Steam in that order.