iPad OS has a feature called Split View. You can use this to put two different apps side by side, or have two side-by-side document windows for the same app.
Photoshop on iPad supports Split View if you want to put a different app on the other half of the screen. For example, you can put Photoshop on one side of the iPad screen, and Lightroom or Illustrator or your web browser on the other side.
However, when I tried the standard iPad OS steps to set up two side-by-side Photoshop documents, Photoshop said “Multiple Windows Not Supported.”
So although iPad OS Split View allows for side-by-side document windows of the same app, Photoshop is one of the apps that does not support that, or at least not yet. If it’s important to you, you can request that feature in the Ideas section of this community.