When there are upgrades available and another application locks the apt database to upgrade packages, muon still shows the upgrade notification. Ideally muon shouldn't show those notifications since another package manager probably is upgrading packages Reproducible: Always
Updates will not start if there is a lock in place, so this is really just an annoyance.
Muon is no longer maintained, please switch no a supported alternative like https://apps.kde.org/discover/ or the package manager native no your system. Sorry for the inconvenience.