Flat pack furniture traditionally had the relationship for being crap, in particular for missing pieces like a screw here or there, but when Ikea came along they did things properly. That was the reason they got so popular, they were so much better than the competition, and they forced others to up their game. I think they were the first to actually include extra screws, to cover the occassions when they weren’t there, but these days their quality assurance is so good they just include the exact right amount every time.
They also have a little depot that you can go to to get extra screws and bits of wooden dowel and stuff.
You can go in tell them you need a type 4 screw from set 10.34.82.14 and they go oh yes that’s a Peürïng, and give you it.
For some reason they also ask how many you need.
I’ve done that once, and honestly wrote I needed four screws. A few days later I got an envelope with like, 20 screws. I get it, but still found it a bit funny.