I use manjaro with kde plasma on two devices, and on one I face this weird issue that when I try to change the icons of widgets in the panel, the ok button is not working. It works on the other device, but here it is greyed out. I have no idea how I can fix this issue. If I open the plasma-icons folder and go to the properties there, it works.
Anyone an idea?
Welcome to the forum! 
It may be related to whether you have installed a global theme or not. Global themes override all other theme preferences, which is why I always recommend not using any global themes, but instead setting the themes for individual sections separately ─ e.g. window decorations, icon set, application theme, et al.
Thank you for your help! But how is it possible to not use a global theme? I have Breath2 2021 but also use all the individual section settings. I can’t deactivate Breath2 2021 - do I have to activate the older Breath2 because it is default - is that equivalent to not using a global theme?
Yes, it’s the global themes from store.kde.org that are often problematic. Breath is based upon the natively built-in Breeze theme, so that won’t cause any issues.
Best is to not select a global theme yourself. Then you can take it from the built-in defaults for theming the individual sctions.
I changed it and don’t use a global theme, but the issue continues. I can’t change the properties. I looked into the systemlog and when I open the properties, I get the following output:
30.08.21 10:29 plasmashell file:///usr/share/plasma/plasmoids/org.kde.plasma.notes/contents/ui/main.qml:202:17: QML Binding: Not restoring previous value because restoreMode has not been set.
This behavior is deprecated.
You have to import QtQml 2.15 after any QtQuick imports and set
the restoreMode of the binding to fix this warning.
In Qt < 6.0 the default is Binding.RestoreBinding.
In Qt >= 6.0 the default is Binding.RestoreBindingOrValue.
30.08.21 10:29 plasmashell Error: cannot change the containment to AppletsLayout
30.08.21 10:29 plasmashell Error: cannot change the containment to AppletsLayout
30.08.21 10:29 plasmashell file:///usr/share/plasma/plasmoids/org.kde.plasma.notifications/contents/ui/FullRepresentation.qml:549:37: Unable to assign [undefined] to bool
30.08.21 10:29 plasmashell file:///usr/share/plasma/plasmoids/org.kde.plasma.notifications/contents/ui/FullRepresentation.qml:444:41: Unable to assign [undefined] to QString
30.08.21 10:29 plasmashell file:///usr/share/plasma/plasmoids/org.kde.plasma.notifications/contents/ui/FullRepresentation.qml:459:41: Unable to assign [undefined] to bool
30.08.21 10:29 plasmashell file:///usr/share/plasma/plasmoids/org.kde.plasma.notifications/contents/ui/FullRepresentation.qml:439:41: Unable to assign [undefined] to int
30.08.21 10:29 plasmashell file:///usr/share/plasma/plasmoids/org.kde.plasma.notifications/contents/ui/FullRepresentation.qml:441:41: Unable to assign [undefined] to bool
30.08.21 10:29 plasmashell file:///usr/share/plasma/plasmoids/org.kde.plasma.notifications/contents/ui/FullRepresentation.qml:461:41: Unable to assign [undefined] to QString
30.08.21 10:29 plasmashell file:///usr/share/plasma/plasmoids/org.kde.plasma.notifications/contents/ui/FullRepresentation.qml:425:41: Unable to assign [undefined] to bool
30.08.21 10:29 plasmashell file:///usr/share/plasma/plasmoids/org.kde.plasma.notifications/contents/ui/FullRepresentation.qml:549:37: Unable to assign [undefined] to bool
30.08.21 10:29 plasmashell file:///usr/share/plasma/plasmoids/org.kde.plasma.notifications/contents/ui/FullRepresentation.qml:444:41: Unable to assign [undefined] to QString
30.08.21 10:29 plasmashell file:///usr/share/plasma/plasmoids/org.kde.plasma.notifications/contents/ui/FullRepresentation.qml:459:41: Unable to assign [undefined] to bool
30.08.21 10:29 plasmashell file:///usr/share/plasma/plasmoids/org.kde.plasma.notifications/contents/ui/FullRepresentation.qml:439:41: Unable to assign [undefined] to int
30.08.21 10:29 plasmashell file:///usr/share/plasma/plasmoids/org.kde.plasma.notifications/contents/ui/FullRepresentation.qml:441:41: Unable to assign [undefined] to bool
30.08.21 10:29 plasmashell file:///usr/share/plasma/plasmoids/org.kde.plasma.notifications/contents/ui/FullRepresentation.qml:461:41: Unable to assign [undefined] to QString
30.08.21 10:29 plasmashell file:///usr/share/plasma/plasmoids/org.kde.plasma.notifications/contents/ui/FullRepresentation.qml:425:41: Unable to assign [undefined] to bool
30.08.21 10:29 plasmashell file:///usr/share/plasma/plasmoids/org.kde.plasma.notifications/contents/ui/FullRepresentation.qml:549:37: Unable to assign [undefined] to bool
30.08.21 10:29 plasmashell file:///usr/share/plasma/plasmoids/org.kde.plasma.notifications/contents/ui/FullRepresentation.qml:444:41: Unable to assign [undefined] to QString
30.08.21 10:29 plasmashell file:///usr/share/plasma/plasmoids/org.kde.plasma.notifications/contents/ui/FullRepresentation.qml:459:41: Unable to assign [undefined] to bool
Any idea what is wrong?
Did you find a resolution to this problem? I am having exactly the same issue.