Hi!
No, you can't submit an .xcodeproj Xcode project. You must submit a .swiftpm App Playground (and zip it before you send it). Keep in mind that you should not use the playground option, but rather App Playground, when making a project. Here's how you can make one:
To make an App Playground on Xcode, go to File > New > Project > iOS > App Playground.
To make an App Playground in Swift Playgrounds, select the "App" button in the bottom left corner or go to File > New App Playground.
Many of the Xcode project features are also available in App Playgrounds, such as adding capabilities from the Xcode's Signing & Capabilities tab.
Make sure to read the rules again when submitting, to check if everything's okay. You can find them here.
Good luck!