First, doesn't Microsoft give away M365 for free to educational institutions? (Perhaps that's only US institutions, though.) Second, isn't this how they bill their accounts — Business Basic doesn't get desktop apps and you need to pay more to use desktop apps? Third, did the OP try to open their document in LibreOffice? I think there's a legitimate criticism of the move from one-time lifetime purchases to the SaaS economy, but Microsoft isn't the only one who deserves criticism for this.