You cannot install a mod over the official Play Store version.
Go to Settings > Security and toggle on Install Unknown Apps for your browser. How to Install the MOD APK Geometry Dash MOD APK V Download [All Unlocked]...
⚠️ Downloading "MOD APKs" from unofficial sources can expose your device to malware, data theft, and account bans. You cannot install a mod over the official
Allow the app to access storage if prompted. Geometry Dash MOD APK V Download [All Unlocked]...
Use a "burner" account if you are worried about your main account being flagged. If you'd like, I can help you: Find official texture packs that are safer to use. Learn how to use the Level Editor to unlock icons legally.
Search for trusted community sites like APKMirror or specific GD modding forums.