While Office 2021 is affected by the expiring license, it's still under support until Oct 2026 and users just need to update. It only reverts to read-only if you don't update.
Thank you. I had been wondering about this precisely because Office 2021 is still receiving updates.
So this is really only an Office 2019 issue. Which still isn't great, but it is at least older.
And from the sounds of things, this only impacts the retail-licensed version of Office 2019. The volume licensed LTSC version doesn't rely on an activation server or certificates.