Several of us engaged in a random discussion while touring France about where in the world you can and can't flush toilet paper -- or anything else. In Athens we were told to never flush toilet paper because their pipes are often too narrow to safely accommodate it. They told us to put it in a bin next to the toilet. Most of us said "ewwwww" but part of traveling the world is getting used to local norms, right? Here's a map I found that shows where you can and can't flush, according to the local sewer authorities.
https://brilliantmaps.com/flush-toilet-paper/
Another page said: "In Europe, you cannot flush toilet paper in Greece, Belarus, Bosnia and Herzegovina, Bulgaria, Cyprus, Macedonia, Moldova, Montenegro, Turkey and Ukraine. Around the world, you are not allowed to flush toilet paper in Egypt, China, and rural South America either. In remote areas, you may be unable to flush paper as plumbing may not be as good as in the cities.
(https://www.explore.com/1480088/dont-flush-toilet-paper-vacation-countries-reason/#)