According to the answer on the Dell support website, installing the Dell touchpad driver or the Dell Quick Set application will allow you to disable the touchpad on your device.
https://www.dell.com/community/en/conversations...
Here are the download links:
Dell Quick Set application:
https://dl.dell.com/app/Dell_QuickSet_A07_R2726...
Dell Touchpad driver:
https://dl.dell.com/input/R253430.exe
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