This is the most common error when sideloading system launchers. It typically happens for two reasons:
Once you have downloaded the APK file from a trusted source and enabled unknown sources for your browser or file manager, follow these steps:
Installing a launcher APK is a straightforward process, but it does require a few steps.
If you need help resolving a specific issue with your device's home screen, tell me: What is your ? Are you trying to fix a bug or install a new feature ? What error message (if any) are you seeing on your screen?
A different version of Launcher3 is already installed as a system app.