Last year it was announced % and # support for file and folder names in Sharepoint Online, according to this link:
To verify that you have this feature enabled you run (using latest Sharepoint Online Management module) get-spotenant |ft special and it should display: SpecialCharactersStateInFileFolderNames : Allowed.
I have this setup on my tenant, and I created a Sharepoint Team Site, from the interface: Create Site.
I then proceeded to create some folders named "Folder%", "Folder#", and put some files inside: "test%.txt", "test#.txt".
By going to 'Document' on the left menu, I can browse the folders without problems and view the contents of the files.
If I try to go to the same place, but using the web part "Document library" that's on the right side of the page, when we click 'Home'. It shows the folders and I can navigate to them, but can't open the files, I have the following error :
This explains the setup:
Is that the web-part does not behave the same as the Documents interface ? I could not find any document in Microsoft's site.