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As I stated in one of my previous blog posts, External sharing in SharePoint is one big matzo ball. Trying to understand external sharing requires lots of patience and alcohol consumption. I tried to explain the concept many times on my blog, and you can find a summary of all the options
Sometimes Microsoft publishes text in message center notifications that is, to be blunt, misleading. Such is the case for MC220791 published August 21, 2020, updated May 7, 2021 (Microsoft 365 Roadmap item 43797). You can see from the dates that this change has been bubbling up for a long time.
If you are a SharePoint site admin, you may need to manage expiring access for the guests that have access to content on your site.