This is the fix for the update issue. The value of “Suite” was changed from testing to stable.
When you update, if you see this message:
E: Repository 'http://raspbian.raspberrypi.org/raspbian buster InRelease' changed its 'Suite' value from 'testing' to 'stable' N: This must be accepted explicitly before updates for this repository can be applied. See apt-secure(8) manpage for details.
Command to run:
sudo apt update --allow-releaseinfo-change