Since the official Google Play Store and Apple App Store only provide the latest version (currently 2.2+), you have to use third-party archives. Use Trusted Archives
Since you aren't using the Google Play Store, you must allow installation from your browser or file manager.
Analysis of Geometry Dash 1.0 : Technical Architecture and Preservation of the Original Build Geometry Dash (GD)
Finding a working APK for version 1.0 requires using reputable archival sites, as the official app stores (Google Play and Apple App Store) only provide the most current updates.
