There is no computer system which is set and forget and Manjaro Linux is no exception.
User intervention is required on a regular base.
Know your system - best practise is individual - you will know.
- [HowTo] Updating Manjaro as safely as possible
- [root tip] [How To] Update Manjaro the smart way
- [Need-To-Know] About Manjaro and AUR
In order to separate any possible issues when syncing your system - custom packages, that is AUR, Flatpak, Snap or AppImage - should be maintained separately.
Always do a base system sync first.
Then launch your custom applications one at a time and verify they are in a working state.
If any of your custom packages has become dysfunctional - especially python based apps - then you need to rebuild the package in question.