If you don't care about ratio distortion, in Project > Settings > Screen, check "full screen" and "resizable" checkboxes.
You can also set the screen.keepAspectRation options to true in the project.pixelbox file (this option is currently not exposed in the editor), but this will add black borders.

To have real fullscreen without pixel distortion, a solution would be to resize the $screen texture at runtime.

Pixelbox editor can't export directly an executable directly, but it can make a Electron prebuilt (Project > Electron prebuilt).  This can be build to an executable. You'll need NodeJS and NPM installed on your machine. Follow the instructions in the generated readme.md file.