Its always dangerous to think Europe is one culture. Doesn't surprise me a bit that yoga pants are appropriate in Prague, and rags in Russia. Because of this topic a few years ago i actually took a count during two performances in Budapest. Neither an opening performance. The last time i think i counted 10 men without at least a sports coat. I am guessing i couldn't see half the guests so the number might have been 20. The place seats about 1500 so that's a minority. Mostly tourists in the balcony; but not all.
My favorite are always the pensioners who pull out their best dress from 1969 and wear it with pride; hats, furs, wide lapels, tired old shoes. Its terrific. The difference might be that when we were at the theater in Vienna and Prague most of those there were tourists. In Budapest, the locals still out number the tourists; its more culturally ingrained. Budapest does have a second venue which is apparently less dressy (and at present it is the only one open).
here is my favorite night at the opera. https://pb2.jegy.hu/imgs/system-4/program/000/074/313/hary-estely-original-86511.jpg