Is the Magic Mouse unpaired from any other device it may have been paired with?
- On iPhone, iPad, or iPod touch: See Unpair a Bluetooth device.
- On macOS Ventura: Choose Apple menu > System Settings, click Bluetooth in the sidebar, Control-click the device, then choose Forget.
- On macOS 12.5 or earlier: Choose Apple menu > System Preferences, click Bluetooth, Control-click the device, then click Remove.
Once its unpaired, it should enter pairing mode, and should be seen by the iPad.
Do note, the iPad must be running iOS 13.4 or later. Use a Bluetooth mouse or trackpad with your iPad – Apple Support
It won't work with earlier versions.