In Steins;Gate 0, it explains how Okabe sent a video message to the past back to himself. What happens to the current Okabe's memories of Amadeus who is in the Steins;Gate world line? I assume nothing ever happened to him meeting Amadeus, but it seems sad because only the Okabe who sent the video file knows about Amadeus. And that Okabe probably doesn't exist anymore.
Seeing as the Virtual Novel for Steins;Gate 0 had not come out during the production of Steins;gate, I would assume the production team would not have included Amadeus into Steins gate.
But to further answer your question Okabe is not an all-knowing entity in that, he knows all timelines, but more that he remembers all actions taken by himself after he has made a new jump using the PhoneWave. Okabe has no memories of what happens to the Okabe he leaves behind after he decides to use the PhoneWave to jump forward or backward in time. He only follows the reaction to the PhoneWave so technically his consciousness follows the timeline of the messages in the PhoneWave.
In simpler terms, the Destination of the messages from the PhoneWave becomes the destination of his mind because he only follows the change in the timeline.
So when he decides it's hopeless to save Kurisu the consciousness of Okabe(Steins;Gate) then leaves to follow the line of the PhoneWave so the Okabe(Steins;Gate 0) is then left to his own devices separated from Okabe(Steins;Gate)
Although future Okabe(Steins;Gate 0) seems to no longer have the special ability to follow timelines seeing as he doesn't follow the timeline back when he sends the video back with Hashida's daughter, Suzuha. But this could be explained seeing as he did not use the PhoneWave to message his old self but instead had someone else go back to try and change things.
I hope this answers your question. I am no philosopher but I do hope that this message is concise and accurate. If I am wrong, I'm sure someone will find a way to points out the flaws in my interpretation.