They're not terribly common even within the US. I refinanced my house recently, and and I had to order a new checkbook from my bank to do it, because I couldn't find the one they gave me four years ago. Every time I do have to write a check, I always have to "figure it out" again, which isn't exactly rocket science, but is a testament to how little I write checks.

Like most of the world, I use credit cards or debit cards or a cash sending app.

They're common enough for banks to universally support them. E.g. if you get compensation from some company (due to overpaid bill, legal settlement etc), it'll usually come as a check by default - and sometimes that's the only available option. I've also dealt with landlords and home repair providers that would only accept checks.

yet you can still cash a check and write a check even if its not popular.