Here is a small assembly that allows keeping opened a window with a closure type handle PVC espagnolette. 7x7mm maneuvering shaft and screw fixing between 43 mm axles.

The idea is to move the handle block to slide the opening along the ribbon, then lock again to block the opening.

A 1/4 turn rotation of the handle locks or unblocks the ribbon thanks to the eccentric, which slides the bolt.

CAUTION: This system does not guarantee tamper-proof blocking. Well, or the opposite, it is designed to be forced and reusable later.