You need to tip places where you sit down to eat with waiters, yes. ~20% of the subtotal before tax. Don't be intimidated by those little tablets asking for a tip for places where there is no table service, there is usually a no tip button. Just relax and don't hit a button right away. They make it a little smaller.

When in Rome…

I only tip if someone had to do something to get me that food/experience. Picking up food to take home? No tip. The restaurant makes you get your own food from the counter and do your own refills? No tip. The checkout screen might have a tip, but I'm putting 0.

It's not really your personal responsibility, it's the restaurant owners responsibility. If people aren't getting enough tips in a restaurant where tips are the big draw, and that causes wait staff to quit, the restaurant owner should be paying his people to subsidize that.

15-20% also is not a hard rule. There's a lot of places where I live that try to pass off costlier food in shitty atmosphere (think 30 dollar entrees, but the server sees you twice and it's a "theme" restaurant). If I think someone did well and engaged with us as customers and were pretty good about making suggestions on the menu or being extra attentive to drink refills, then guaranteed they're getting within that 15-20%. Anything less than that, then I as the customer who only gets to make that judgement call off of the limited interaction we have, and you'll get 7-10% or 5 bucks, whichever is bigger.

I already replied but I just wanted a top level comment regarding:

that extra expense in a country where everything is already so expensive really makes a difference

That tip expense would be paid either way. There's no difference between charging $9 for a sandwich and tipping $1 vs being charged $10 for the sandwich and no tip. All costs always get passed down to the consumer no matter what, that's just how it works. So it isn't an "extra" expense. It is, was, and always will be in there, one way or another. I agree tipping is weird, inefficient, and difficult to understand, but you're gonna pay no matter what.