There are various restrictions and limitations that apply to file names and file types when syncing with OneDrive for Business or SharePoint in Microsoft 365.

Microsoft publishes a full up-to-date list of restrictions here.

Invalid characters

Certain characters have special meanings when used in file names in OneDrive, SharePoint, Windows and macOS, such as "*" for wildcards, and "\" in file name paths. If a file or folder you are trying to upload to OneDrive contains any of the characters listed below, it may prevent files and folders from syncing. Rename the file or folder to remove these characters before you upload it.

" * : < > ? / \ |     (Leading and trailing spaces in file or folder names are also not allowed.)

Invalid file or folder names

These names are not allowed for files or folders: .lock, CON, PRN, AUX, NUL, COM0 - COM9, LPT0 - LPT9, _vti_, desktop.ini, any filename starting with ~$.