Also, you really have to make a clean break. Users are comfortable with what they know. If you leave the door open to use the old-and-familiar, they will fight changing to the new. Train them on LibreOffice and then take away any and all access to MS Office.
They will keep using everything else that is touched by Microsoft.
Github, Typescript, Windows, Active Directory, Open AI servers on Azure, Visual Studio, possibly contractors using .NET, npm infrastructure,...
(Actually 15 years is mentioned in the article now that I scanned it)