Summary

A simple solution to keep my cat from opening a mosquito net window screen.

Part 1 - curved at 25 mm R, should fit a standard PVC/Aluminium window frame.
Measuring block 30mm - mark with a pencil and then Cut/Extrude the bottom part to make the height equal to Part 1 so that the cover fits.
Cover - a bit difficult to put and remove and can get deformed in the sun (extrude the top to make it sturdier).
4 x 30 mm length / 6 mm diameter screws are needed to fasten the latch to the window frame
if the Measuring block needs to be cut more than 15 mm 20mm screws can be used instead.
You'll need a drill with a 2 mm drill bit to make the holes in the window frame and screen.

I printed this in PLA and it seems strong enough to hold the screen firmly shut without gaps.
only Part 1 Requires support if printed as shown (or print it on its side)

Put in 2 corners and close to the middle for best results, for this you'll normally need 3 measurements with the Measurement block, because screen nets like these are never equally centered onto the window frame.

This will not work directly for your window. Some underextruding or cutting in the slicer is required.