I there a problem trying to click on low, medium or max  to select the autobrakes.

Cannot seem to do it.

Do you need engines running to select it?  Aircraft is powered up

What phase of flight are you in?

Do you have a TCA throttle and all the addons? I noticed the Auto Brake setting on the left addon over-rides pressing the button.

You need autobrakes (max) at takeoff and medium-low during approach.

Why would you set them while the engine is off?

Just at gate, have to read checklist better.