This change would go against multiple consumer guarantees in Australia where it's 1) a right to have undisturbed possession of a product 2) products must be fit for the advertised purpose https://www.accc.gov.au/consumers/buying-products-and-servic... Microsoft would be breaking consumer law if the change goes ahead for the perpetual licenses they sold in Australia
Also, it's Office 2019, but they were officially selling it until the end of 2021, and third-party sellers were selling through their boxed inventory for years after too. So, this isn't even that old a piece of software.
And, let's not forget, this is trillion dollar corporation. They could find one of their Mac devs to write an update for this in a week. The negative publicity from this is measured in millions of dollars.
And this won't be their first time breaking Australian Consumer Law... Twelve months ago no less!
https://www.accc.gov.au/media-release/microsoft-in-court-for...
The ACCC is going to love this.