Photoshop doesn't go on full screen

You can zoom in and fill the gray box area with your artboard, if you would like.

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@eleonoras71549224 wrote:

Why they can't go full screen.

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Photoshop uses its own Full Screen mode, not the macOS full screen mode. 

Full screen using macOS uses Spaces:

https://support.apple.com/guide/mac-help/work-in-multiple-spaces-mh14112/mac

See the reply from Senior Product Manager @J453 for the official explanation as to why Photoshop does not use Spaces:

https://community.adobe.com/t5/photoshop-ecosystem-ideas/p-support-for-native-full-screen-mode-on-macos/idc-p/12263719#M11057

To use Photoshop's full screen mode, you can use the View menu > Screen Mode or the keyboard shortcut "F" to toggle between the three modes. Escape will also take you back out.

https://helpx.adobe.com/photoshop/using/viewing-images.html

Jane