I posted on the linked thread about opening Lista type cabinets and a couple other threads on the same subject. I had to open several every month at work but I have been retired for 10 years so I have forgotten details.
Most cabinets have a lock bar vertically up the back of the cabinet, either in the center or at the corner. If you look through the small gap at the top of a drawer and shine a strong light through the same gap you can see the lockbar. Most lockbars flip to one side, some raise to release. I kept a piece of 1/8" x 1/2" or 3/4" flat strip handy to slide through the gap and flip the lock bar. Depending on the design a locked cabinet (as with a key) may not allow the lockbar to move. Our cabinets were never key locked, they usually jambed the lockbar when they slammed the drawers shut.