Unable to adjust display brightness

I cannot change the brightness of my Macbook Pro 14" 2023, M2. I.e. the brightness bar in the system preferences/displays window is inactive and set to full brightness. The option to adjust brightness automatically is also inactive and isn't turned on. When pressing the brightness keys on my keyboard, the brightness symbol appears together with a lock indicating that the settings are locked. Why is that?? Could it have something to do with the latest update to Ventura 13.5.1? Or does it have something to do with the display settings? I need to adjust the resolution to get larger text, since my eyes are bad and the 14" display is small. I tried to set the display resolution back to standard, but the problem remains.

I am using a LG external screen but the problem appears with and without having connected the Macbook to the external screen.

Grateful for any suggestions beyond how to adjust brightness with the brightness bar and changing the display settings. Thanks.