You installed an older cached version. Delete the app completely (hold icon > Remove App > Delete App), then re-download from the App Store. Ensure your iPadOS is updated.
Because it uses —the same code used by professional developers—you will never "outgrow" the app; the skills you learn here are directly applicable to professional software engineering. Swift Playground - Apple Developer Swift Playgrounds 4.1 Download
The on iPad is straightforward, but following these steps ensures you get the correct version. You installed an older cached version