Answer by Simon_Weaver for How to check if ios safari/chrome is in lockdown mode for a ReactJS Webapp

I'm using this:

if (typeof window.FileReader === 'undefined'){     alert('Do you have Lockdown Mode enabled on your device?\n\nIf so you will need to add our website to the list of allowed sites to continue.');}

Any false negatives or positives observed for this would be appreciated.