Mouse Support is a Paid feature. There is a FREE trial for two days. After that you will need to purchase KeyPad to continue to use it.
Press Control+Option with KeyPad window active to trigger the mouse.
Video of using KeyPad with a mouse on the iPad pro
If this is the first time you have setup KeyPad
With the keypad window active, press control + option key together, and then release them. This will toggle the mouse feature.
Now any movements that you make with the Mouse or Trackpad will be sent to the connected device. The mouse cursor will stop moving on the Mac.
To turn off the mouse, press control + option again. The mouse cursor will start moving on the Mac again.
Please remember to close the settings app in the iPhone or iPad. And also close the System Preferences on the Mac. For some reason, having these apps open degrades bluetooth performance for the mouse.
Using Mouse with the iPhone
The iPhone does not have the Mouse feature available by default. To use the mouse you need to go to:
Settings | Accessibility | Touch | Assistive Touch
And turn on Assistive Touch.
Control Control + Option with the KeyPad window open and the mouse cursor will lock to the botton of the KeyPad window. You will now be able to use the mouse to Control the iPhone.
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Do let me know if you face any issues. Please email email@example.com. I update the Support pages regularly, you could check for solutions there too.