Cannot utilize all the functions of the first-generation Magic Mouse.

Unfortunately the first generation Magic Mouse cannot be made "compatible" with your iPad.

You might instead consider replacing the incompatible Mouse with an Apple second generation Magic Mouse, or a simple third-party Mouse - or alternatively consider a current Apple Magic Trackpad.

You should note that any Mouse (or other third-party device) that is reliant upon installation of device driver software will not be fully usable with iPad. iOS/iPadOS does not support installation of device driver software - except thorough installing a manufacturer-provided App.

The first generation Apple Magic Mouse (with removable AA batteries) is not compatible with iPad.

By contrast, the second generation Magic Mouse (rechargeable) is fully compatible with iPadOS.