I worked on older versions of SharePoint where we can upload different file types which were not supported in SharePoint online. Normally user face this issue during migrations from older version.
Restricted Characters in file/folder names
Below is the list characters which you can not used in file name or folder name in SharePoint Online and OneDrive:
- ” * : < > ? / \ |
Unsupported file names
Below is a list file names which you can not use in SharePoint online or OneDrive:
- .lock, CON, PRN, AUX, NUL, COM1 – COM9, LPT1 – LPT9, _vti_, desktop.ini
You can use ~ at the start of folder name as it have different meaning SharePoint and also can not use Forms folder at the root of document library because there is already a default forms folder at the root of each document library.
Restricted File types
Recently Microsoft have removed the limitations on file types that can be added. You can save all file types in OneDrive and SharePoint online but they will not work until unless your sharepoint site allows to run custom script. Custom script is blocked on SharePoint online root site collection and also on group sites. Below are a few filetypes which can work if custom scripting is enabled:
.aspx, .asmx, .ascx, .master, .xap, . swf, .jar, .xsf, .htc