Bug 497551

SUMMARY
If I have some widget from KDE5 as some standardized function like "launcher" or "system clock", and this widget is not compatible with KDE6, then after updating to KDE6, it will not let me select "alternatives" for it anymore.

Getting a widget for the same function (e.g. launcher) requires removing said widget from the system panel and adding a new one instead, which has the side effect of **deleting the user's config** for it, thereby preventing one from updating the widget while keeping the same config.

STEPS TO REPRODUCE
1. Install a KDE version from the 5 series.
2. Install a custom widget for application launcher, such as this one: https://github.com/adhec/OnzeMenuKDE
3. Configure said widget to be your application launcher, by right-clicking the current one, selecting 'Show Alternatives', and choosing that 'Onze Menu'..
4. Upgrade everything to KDE6.
5. Restart computer.

OBSERVED RESULT
The widget doesn't work, and it doesn't let me select an alternative for application launcher when right-clicking it. It's worse when it's a highly customizable widget that has updates for KDE6, such as this other one: https://github.com/orblazer/plasma-applet-resources-monitor ; as then removing it loses one's config.

EXPECTED RESULT
Should at the very least let me choose an alternative for the launcher / clock / etc. if the current one doesn't work anymore. Ideally, should offer me to update if there's a new version supporting the latest QML / KF / etc.

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
(available in the Info Center app, or by running `kinfo` in a terminal window)
Linux/KDE Plasma: 
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION