First note -- I already stated that masks were not generally used in Europe
However each country in Europe sets their own standards. Some, like Germany, has each region/state set their own standards for schools and mitigation measures. Generally most countries are following WHO & EU guidance for schools.
For the most part -- masks are not being used in schools in Europe since masks are not required when community spread is low AND the schools in Europe go remote when community spread rises above low.
This -- once again -- is very different situation than the U.S. where community spread is currently high everywhere and we are trying to hold in-person K-12 classes in an environment where Covid cases are common.