It depends on the vendor of the exam too, our proctoring sdk works on chrome and Firefox which means all major OSes too, we try hard not go outside browser context, we support android and iOS natively.
However many exam apps are very poorly written and have limited support for different OS, and usually never for mobile. I have seen full flash apps used today with 3months to deprecation.
we do face detection but not recognition and recommend using human live proctors for high stakes requirements.
The OS vendors are doing their part as well, we partner with both Apple and MS and give constant feedback, Apple announced AAC mode this WWDC and MS had number of APIs
Linux support is a factor in the education assements space due to chromebooks, most of my devs and half of my ops use linux , so I can say atleast one vendor cares.
Today there is profussion of vendors and overnight shops attempting to build in this space post covid-19, sales here is like any other enterprise product , tech merit is only one component, and nuances are lost on the customer in the hurry post covid 19, exam/certificate bodies have little scrutiny and rarely choose the better product for the user.
However in few years things will improve, buyers will understand the tech better, vendors will consolidate.