need help removing a fixed screen net 😭😭😭

I'm losing my mind.

I need to remove the fixed screen net in my kitchen to access the glass window behind it.

There are two plastic parts at the top showing left-right arrows. By sliding both away from the window frame, I can somewhat unlock the upper part. I can't remove it completely, but it moves a bit (both sides). This is not the case with the plastic parts slid toward the frame.

However, I have no idea how to go from here.. I don't see other obvious "locks", but nothing budges.

Any suggestions?

(I don't know the manufacturer of the windows/screens unfortunately)