We live in Denia, Costa Blanca and are just starting our second summer in our home and clearly a second summer of having to deal with these pesky nuisances. We are reasonably certain that the flies are known as sewer or drain flies and look almost like “Dumbo-style” and are very slow or stupid or both! Fortunately they do not bite nor they appear to be interested in foodstuffs. All of the advice we have read covers treating drains, sinks etc but there is a significant difference in our case - these appear to be trying to get in our house via the windows/bug-screens and do not necessarily emerge from sinks and plugholes inside our home. We have newly installed bug screens which do a great job on regular house flies and even mosquitos but these manage to get in.
I am hoping that through this forum we may find someone else who has endured a similar problem and hopefully overcome it.
Does anyone know of any solution which can be applied surrounding the screens to help their efficiency against these little monsters or of any specialist forms (preferably English-speaking) who may have some useful advice.
Heres, hoping?

Sorry, I can’t offer a solution, just a story from when I was living in Doha, Qatar… your situation reminded me of my stupidity in not putting two and two together
For months I had these sewer flies, like you say flying ‘Dumbo’ like around the bathroom… where did they come from, why were they there, were they going to kill me? To be honest I had more success killing them - they are almost sitting targets, but after a while I began to be concerned about karma!... and was diverted by a bit of a sewer smell. I called the maintenance guys around and they stopped a gap between the trap and WC… didn’t work. Called them out again, and again, and again…

Doh!... dawned on me, the bidet trap had evaporated. I mean who uses those things? What a waste of ceramic. I turned the tap on for thirty seconds: the smell went and not a single fly came back.

I only hope your solution is as simple

Thanks Tim, though our bidet is in the least affected bathroom so not sure there is a link. Nonetheless it is certainly worth a shot and I shall do so!