You are running a Dexter Industries and/or Modular Robotics operating system based on Buster and when you attempt an apt-get update, you see the following error:
Repository 'http://deb.debian.org/debian buster-updates InRelease' changed its 'Suite' value from 'stable-updates' to 'oldstable-updates'
. . . and it mentions that it must be explicitly authorized.
The solution is simple:
Just run. . . .
sudo apt-get update --allow-releaseinfo-change
. . . . in a terminal window, and the problem is solved!