Hi @john john ,
As said in the quoted sentence: when a user shares or stops sharing an item that contains other items with broken inheritance. This sentence may only apply to item level. I created a folder in a document library and uploaded a file into that folder. Then I stopped inheriting permissions of that file. An user who has permission to the folder but doesn't have permission to the file couldn't access to that file. Then I shared the folder with that user and found that the user can access to that file with unique permissions. Also, I tested your process in my end. Same result with you. So, I think this sentence may only apply to item level instead of list/library level.
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