Not the USA for sure. One reason taxes are complicated and full of loopholes is to allow rich people to game their taxes and pay next to nothing. They have enough power and influence and their incentive is to keep things as they are: complicated.

This could be a number of European countries

Works the same way in France, too, for regular salaried income.

If you have other income, like dividends, there are a few more boxes to fill, but it's still fairly simple.

Once you start having serious money, you better have a tax lawyer doing this for you, but I suppose this is the case everywhere.

Several European countries. In the Netherlands taxes are just logging in to a web interface and verifying the provided data.

It's usually filed correctly already. So many times you'll just be clicking next.

Could be Australia? Looking at others commenting though could be a lot of other countries.

The USAs tax system where the online portion was essentially privatized by a single company (Turbotax) was pretty jarring.

It works this way in Sweden. Not sure which country he was referring to.

My taxes in Spain were pretty much like that. You get a letter with the government's estimate. If you agree, you don't have to do anything else.