To answer the original poster's question...
The screens in the picture are commonly installed on gas furnace air lines to prevent things from crawling into the pipes. They are not used on the condensate drain line. These pipes are air for combustion, and the exhaust. Currently, air pipes are 4" dia, but these look to be older, a smaller diameter.
DO NOT follow advice here to put in a P-trap, or flush these AIR LINES with anything.
The screens pictured are good because they have a much larger total surface area than the pipe cross section. Better screens will have openings in the screen that are a bit smaller, and larger overall screen surface area to reduce the pressure restriction that comes with adding a screen. These screens have a large volume of air moving through them.
Condensate lines are usually 3/4" or 1" diameter. If you can find a screen that diameter, and put it on condensate line, it may prevent some things from getting in. A gecko can squeeze thorough a very tiny opening. If you make a screen with tiny holes the size of window screens, it would likely plug up. I would not stretch a window screen across the opening of the PVC - that's asking for problems.
Any screen you add must be stainless steel.
Might want to look into this
hXXps://pvcventscreens.com/product/svc-is075/
https://pvcventscreens.com/product/svc-is075/