New answers tagged security-trimming
Site owner can not view site from Viewer's angle. Your given permission must be appeared whenever you login in a site. When I test permission in sites, I used to create several users like Editor, Reader, Admin and so on.
OOTB he can't, the best option is to have a test account(s) for this purpose where you can log into a PC or run browser sessions as that dedicated test account and get the same experience as the other users. He only has the option to go through lists and libraries looking for broken permissions and doing effective permission lookups.
It would pay to clarify if your view is set to Show or Hide folders. Modify your view, then scroll down to the Folders Section. Make sure "Show items inside folders" is checked rather than "Show all items without folders".
Have you looked into Creating Document Sets? As you can give individual access to each Document sets . Better option then using folders.
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