This Bug is caused by upgrading from packagekit_1.2.5-3_amd64.deb to packagekit_1.2.6-1_amd64.deb when it migrated to testing on 2022-12-07. I downloaded the latest 1.2.5* version from https://snapshot.debian.org/package/packagekit/1.2.5-4/#packagekit_1.2.5-4, downgraded and apt-pinned it and:
-> package-update-indicator works like a charm as it used to do since long So this Bug should be assigned to packagekit_1.2.6-1 rather.
