
According to my experience, here are some naming convention policies of files or folders for you refer to:
1.In the SharePoint Online, the entire file path should not be more than 400 characters which includes tenant name, site name, file name and folder name etc.
2.Do not use illegal characters ".", "()", "/", "&", "!", "#" and etc.
3.Use short names or set titles with characters and spaces in mind, such as: finance-hr-emily.
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