How to Customize Lock Screen Shortcuts on the OnePlus 3 and OnePlus 3T
The most simple method - and I've tried this on my own OnePlus 3 running OxygenOS Open Beta 21 - is to simply disable the stock camera app - known as "OnePlus Camera" on OnePlus devices.

To disable it, go to Settings &gt; Apps &gt; OnePlus Camera &gt; Disable

That should do the trick.