There are 2 types of toilets, siphonic and wash down. Wash down toilets don’t necessarily use less water but they are usually capable of 2 different volumes of flushing. There’s 2 buttons to flush, one uses more water than the other. The big flush is basically the same amount of water as a siphonic toilet but you have the option to use less water. Siphonic toilets don’t support 2 different flush sizes. If you have 2 different ways to flush, you have a wash down. Wash down toilets are also less prone to clogging.

It’s not quite as cut and dry as American vs European since siphonic toilets do exist in Europe and wash down toilets have become a lot more popular in America.

There were attempts to make siphonic toilets use less water but they were terrible. I have no idea if the rest of the world uses them but America has abandoned them in favor of wash down toilets. Other countries have standardized on wider drains (not sure how common this is) which might make them work better in other places. But I have no idea.

It’s there to avoid splashing toilet water.

Australia, IIRC, standardized on larger drain pipe sizes, so of course your toilets don’t clog. For some reason only some commercial buildings use the larger standard here. As for water usage, my toilet uses 1.3 gallons per flush, and they sell more expensive toilets that use much less but have a stronger pressure system. If/when this toilet breaks I’ll be getting one of those most likely.