I am unable connect my magic mouse to my Mac.

You're welcome. A Safe Mode boot is somewhat the "first responder" fix for many irregularities.

Try connecting the Magic Mouse with its charging cable and rebooting. Then disconnect the cable and see if the mouse is recognized.

If not give this a try: boot into Safe Mode according to How to use safe mode on your Mac and test to see if the problem persists. Reboot normally and test again.

NOTE 1: Safe Mode boot can take up to 3 - 5 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

NOTE 2: if you have a wireless keyboard with rechargeable batteries connect it with its charging cable before booting into Safe Mode. This makes it act as a wired keyboard as will insure a successful boot into Safe Mode.

Have you installed and run any "cleaning", "optimizing", "speed-up", anti-virus or VPN apps on your Mac?

I was trying all sorts of things to get the mouse reconnected and this is what did it! Such a simple solution and I overlooked it. Thank you so much!

There is no such thing as a "device manager." Does the mouse not appear in the Bluetooth Settings?

And, there is no independent software for the Magic Mouse. It's all part of the OS.