Mouse disconnects

Hello BM2400.

Thank you for using Apple Support Communities. It sounds like you're experiencing issues with your Magic Mouse. Specifically, it's disconnecting from your Mac. We can understand how this would be an issue. Allow us to investigate this issue and assist in any way we can.

It does sound like you've done a great job in troubleshooting this specific issue. We'd like to make sure we isolate this issue further. If possible, are you able to connect your Magic Mouse on a different computer? If so, does it continue to disconnect when using it with that other computer or does this issue only occur with one specific computer? We would like to share a helpful resources with you below:

If you can't connect your Magic Keyboard, Magic Mouse, or Magic Trackpad to your Mac - Apple Support

Resolve Wi-Fi and Bluetooth issues caused by wireless interference - Apple Support

You'll find great steps you can try and also information on possible Bluetooth interference. Additionally, you can try to rest your Bluetooth model and also factory reset all connected Apple devices to see if that helps with your Magic Mouse. While having your Magic Mouse connected to your Mac, hold down Shift+Option keys and click on the Bluetooth icon in your menu bar. You will see the options listed to reset your Bluetooth module. This would be a great step to attempt to further isolate this issue.

Feel free to keep us posted on your results. Best of luck.