Various programs and settings (GUI) stopped aksing for password, simply saying not authorized

I did search the forum, but could not find the answer.
since a week ago my Ubuntu Mate 20.04 started presenting a weird behavior. Any activity using graphical tools that require authorization is simply not working. Gparted is not launching selecting it in the main menu, external HD is not mounting, Software center fails to install any packages, any item in Settings that requires sudo privileges is not working or greyed out (for example changing HD mounting parameters).
When selecting/clicking on the option, for example install a package in Software, the program simply says "no privileged aces" or "no authorization", without showing the password input window.
At the same time the command line/terminal works perfectly fine. I can execute any sudo commands, use apt, use pkexec to open the above mentioned programs.
Really need help here. I suspected something is wrong with policykit, but could not find any answers on this or other forums.