Sharing violations occur when Excel detects that the file you are attempting to save is already open by another user or program with write access. This protection mechanism is in place to prevent data conflicts and maintain file integrity. When Excel identifies a sharing violation, it restricts your ability to save changes until the file is no longer in use by another user.

 https://livehelpbook.com/solved-cant-save-an-excel-file-on-a-sharing-violations-of-mac/