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Microsoft is killing Office 2021 in October to push you onto Microsoft 365, how to fight back
(www.windowslatest.com)
This is a most excellent place for technology news and articles.
Have you tried Scribus? It's a good open source alternative to Publisher and if it meets your needs it could spare you having to do a lot of faff around trying to keep Publisher going into the future.
But I get wanting to stick with something familiar. It's unlikely you'll lose access to Publisher in the short term. But I'd consider moving to something else now so you're not scrambling should Publisher stop working for whatever reason.