Mouse Lagging on Mac mini

I am answering this to myself so others can see this also. It took me years to finally solve this issue:

My Mac mini 2018 had issue with mouse lagging. It happened after many OS upgrades. And every upgrade it's getting worst. Especially when I am downloading and uploading large files, the lagging came to a point where my Apple Magic Wireless Mouse was almost unusable. This is due to internal WiFi chip is interfering with internal Bluetooth chip. My guts feeling is that internal WiFi chip and Bluetooth chip are actually one combo chip. When Wifi is heavily used, MacOS reduces performance on the Bluetooth part to prevent the chip from overheating and melting. Believe it or not, chip overheating and melting did happen to my Dell Alienware Alpha R1 compact PC a few years back. I took the PC apart to find out why internet is not working and I realized it's the WiFi/Bluetooth chip was melting and died.

So the solution is use an external bluetooth hardware such as StarTech Bluetooth 4.0 USB Adapter (USBBT1EDR4). You can purchase it here from Amazon. This Bluetooth USB dongle is 100% compatible with Mac mini. It works out of the box. First, you will need to shut down your Mac, plug this Bluetooth USB in and then start up your Mac. This Bluetooth USB will override and disable internal bluetooth automatically and it starts up as clean slate bluetooth. So you will need to turn off-and-on on both Apple keyboard and mouse in order for the new Bluetooth USB to discover them. Make sure you have a wired mouse handy so you can activate your wireless mouse at least. This external Bluetooth USB helps to lift up the burden on the internal WiFi/Bluetooth chip.

By adding this external Bluetooth USB, it solves the mouse lagging issue.

You are welcome. I tried many of them for the past years and all the tricks that I could find. None of them solves the issue. Many articles are just speculation especially pointing finger at signal interference are the easiest excuses. My Mac mini is 1 foot away from my wireless mouse and it was lagging. There is no excuse to this. There was nothing in between my mouse and my Mac to be interfered with at all or even around them. Since this external Bluetooth USB works so well, it says a lot about what was wrong with the way this Mac mini is built (and the Dell PC I mentioned above). The speed and workhorse of WiFi today is pushed to the maximum and it jeopardizes the Bluetooth sector of the chip. Luckily MacOS controlled its temperature in order to save my Mac vs the Windows PC did not. For bigger machine, this may not happen because they have a better ventilation which already saves the WiFi/Bluetooth chip from overheating without the OS intervening by reducing bluetooth performance.