Last updated stays on 'this week'.
My version is 15.1.2
It seemed to work before, but the 'timestamp' when I click on Update Link remains 'this week'. I remember before it said something like 'X minutes ago'.
The issue has been fixed in the latest release of InDesign – InDesign 2021.
Please update to this new version of InDesign to get the fix.
Adobe InDesign team