This is the shutoff. It’s stiff from never being closed.

thanks! So can I use that to lower the pressure? Do I turn it clockwise?

Yes, turn that valve/lever toward the front as if shutting off the water supply. It's probably a 90° valve so turning it 90° forward will fully shut off the flow and there may not be much range to adjust it between off and full on. Refrigerator water dispensers (and ice maker fill valves) typically have an internal component that moderates the flow to a reduced rate over a range of supply pressures, which also may make it tricky to adjust.

Thanks! I was able to turn it. I was afraid to do so because it it was pretty sticky initially and I felt like it was going to break the plastic bracket that was holding the valve. But I was able to turn it quite a bit. Water is still on but the flow is more moderate.