I believe (hope) QBDT 2021 will be supported. I saw a press release this Summer stating versions 2020 and earlier are no longer going to be supported...

https://quickbooks.intuit.com/learn-support/en-us/help-article/feature-preferences/quickbooks-deskto...

They state in the release that "We notify you in advance (through email, in-product notifications, the mail, and this page) as services for older versions of QuickBooks Desktop are scheduled to be discontinued." and I never received such a message for QB 2021, so it would be a blindside.