May I missed something but I would need to prohibit users to look through their Windows 10 Computer during taking their exams.
It is possible when a third party programm like Word or Adobe Reader (for example to fill in Words/sentences in forms) is used to take a exam. Also web browsers with "upload" functionality has this problem.
You can open documents on your hole drive. This is also possible when saving documents by right click and "open document". Of course only the allowed programms work. Unfortunately it often is the same used in exams. May there is a way to force users to only open and safe their documents in a predefined folder. (For Example 'C:\SafeExamBrowser\Exams' or something like that)
It is technologically not feasible to implement something like this. We cannot restrict access to parts of the file system, you need to use managed PCs or a virtual machine technology if you want to use complex applications which access the file system or the internet. Read the manual, it's explained there:
https://safeexambrowser.org/windows/win_usermanual_en.html#ApplicationsPane