In the meantimeI have not yet received any feedback from Larian. I have also tried the instructions with the assistant controller and the internet turned off. Is it possible to play as a different character while using the Assistant Controller? I couldn't figure it out and that's why we abandoned the idea as it's also impractical when one person is steering left and the other right. Turning off the internet didn't work at all in fact it had the opposite effect. When the internet is disabled the multiplayer option in the main menu disappears forcing us to reassign characters through the camp. That was no option fur us because yesterday we experienced the worst lag and freezes ever!
Without giving away any spoilers we are relatively close to the end of Act Two and it got so bad that we almost considered quitting the game. However we pushed through but I must say it was absolutely no fun. I felt more sad and frustrated while playing.
But then the closer we got to the end of Act Two the better the performance suddenly became. For the first time yesterday and after 60h gameplay we experienced smooth animation of a summoning spell in split-screen mode. lol
I could also suddenly switch between characters without any issues.
However during combat I had the problem that one character could no longer move at all. The indicator was missing. Attacks worked so he could move through attacking but regular movement was impossible throughout the entire battle. Tomorrow the next patch is set to be released and I hope it addresses the performance issues on the PS5. I haven't found any information about what the patch includes yet except that it's supposed to be quite large once again.