So the game collects data on it's players. It then generates an AI based on that data.

They exist within the game once the game is loaded, keeping the PlayStation on means they can keep living but it's a life of confusion. Much like waking up suddenly 20 years in the future, we all know how that feels. They probably have trouble distinguishing between their real world counterpart and themselves (an AI duplicate).

Lina is the boss, she was built to be an overseer in the system (a ghost in the machine). The company being named after her.

When the game was tested. All the testers in the credits (the Petscop Kids) had their data collected and were recreated as AI sprites. These became Lina's Petscop Kids, making her mother.

Care is Paul. Care's AI sprite was put into the machine and split into three pets or her AI became the three "A,B and NLM" via Rainer's methods. So Care was lost to Lina. She has been waiting for Care to return.

In 2017, Paul plays the game and the new AI is created as a result, this is Paul/Care and thus the last scene is Belle explaining that they are AI (remember being born?) and that Lina has been waiting for her children to return to her. Belle was stuck in the Quitter's Room and Care was taken from her and now both return.

What about the car story? The car that hits Paul did NOT run him over but smuggled his sprite away to the school. When Paul reloads the game he finds the house which maybe what is referred to in Belle's dialogue in the last scene.

This is why Paul does not have a voice, it's not him but the AI version of him. His real self just loaded up a save and carried on.

Belle and Paul are investigating in the real world and now the AI versions are returning their digital home to investigate on what they've missed out on the last 20 years.

Marvin's AI is trying to rebirth Care correctly to the point that he is locking AI up and somehow hurting them if they don't help.

There is lot more going on which I can't make any sense of. Mike, Anna, Tiara, Tool, the de ja vu in the bathroom etc.