Cannot shut down using the logout action button

I have openSUSE Tumbleweed with XFCE installed on my laptop and always keep it up to date. Since a couple of days shutting down the laptop no longer works. When I click on the logout action button and select “Shut Down” it will actually log me out and show me a login dialog again. The laptop stays powered up. Pushing the hardware power button (on the docking station) does work and shuts down the system properly.

I also see a couple of other issues and my gut feeling is that they all have the same root cause. Installing system updates using the normal application no longer works. It will say that updates are available, but when you hit the install button it will say that it doesn’t have the necessary privileges (or words to that effect) to do the update. Logging in as root and typing"zypper up" works.

When I insert a USB stick, it is no longer auto-mounted (that is the configured behavior and did work in the past). The USB stick is shown in Thunar, but when I try to mount it there it fails with the message “Not authorized to perform operation.”

All of this is on the console when the laptop is connected to the docking station.

I assume this is a polkit issue? Can anybody tell me how to resolve this?

Can you quit from the login screen?

No, all options are greyed out there.