Your support.microsoft.com link does indeed say "Rest assured that all your Office 2019 apps won't lose any data. ", and no longer says "Rest assured that all your Office 2019 apps will continue to function". If you cannot edit or save documents, that is not continuing to function. The support document is eliding the biggest change.
According to https://consumerrights.wiki/w/Microsoft_Office_2019_for_Mac, Microsoft sent email to users stating:
"Starting 13 July 2026, a security certificate update is required to keep Microsoft 365 and Office apps current. Since you have a device that cannot support this update, Word, Excel, PowerPoint, Outlook, and OneNote will switch to view-only mode. "
That seems pretty definitive. And this "cannot support this update" bit is completely untrue.