Yes, that is possible. The Odyssey G9 supports both PBP (Picture-by-Picture -> side by side, 2x 27" (2560x1440)) and PIP (Picture-in-Picture -> overlapping, known from TV).
Quote from the German product page of Samsung:
"Thanks to PBP, you can display two sources simultaneously in their native resolution. In addition, with PIP you can scale the size of the second source to up to 25% of the screen. Plus, you can easily split the screen with Samsung's Easy Setting Box SW software."
https://www.samsung.com/ch...

Hello, I have a small question. Is it possible to connect 2 PCs to the same screen and have the image of the 2 PCs on the screen at the same time?

PBP possible but is it possible to set 3 screens ?

I have just learned that the Odyssey G9 can only display 60 Hz in PIP / PBP mode. The much cheaper predecessor still managed 100 Hz.