How can I release these drawer slides?

I’m trying to remove my cupboard drawers and my own efforts have failed, as have my Google searches. Here are images of what the rail looks like:

The black plastic part has an arrow pointing towards the right (towards the back of the drawer). I’ve tried everything I can think of to get the plastic to move, but it doesn’t budge. Note that I’ve tried prying on the plastic, but not super forcefully.

I’ve also tried other tactics, such as looking for levers, catches that can be pulled, screws that can be removed, etc.