ModemManager works well. The update didn’t disable ofono or enable ModemManager in systemd. Now data and SMS work. Calls don’t work because the plasmaphonedialer crashes before it is started completely. So does kclock. Error message looks like this:
file:///usr/lib/qt/qml/org/kde/kirigami.2/private/RefreshableScrollView.qml:175:13: 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.
Updated more packages with pacman and compared all packages with the list from here in kdiff3. No idea what else could be wrong.