There are CERTAINLY some fantastic open-world games that have come out since then. Personally, my favorite, and it's a hot take, is Tears of the Kingdom, but even I can acknowledge where that world falls short.
What Skyrim's world does so well is REALLY encourage exploration. There is something to do literally constantly. Like Breath of the Wild / Tears of the Kingdom is a visual treat, there's not a lot to get side tracked with, and when you do, the rewards aren't always the best.
Where Skyrim nailed this process, is this excellently crafted rhythm of side quest > leads to dungeon > leads to rewards / boss / special chest / ability > leads to dungeon exit > nearby cave / location on your compass. You're coming off your high from the previous dungeon / cave and see another thing to tackle for more things. Maybe this dungeon has a little alchemy or enchanting table where you can mess with that for a minute. Hell, it might even have a full blown forge with materials and everything.
Like there's ALWAYS SOMETHING leading into SOMETHING leading into SOMETHING and you're going halfway across the map in the wrong direction from the main quest because screw the main quest man, I need to find out what's in that GD cave.
I know Skyrim is 14 years old now, (gag). But in terms of Bethesda games and the hate Bethesda has gotten in the last few years, it really has aged well. I think it truly set a fantastic standard that other open world games just don't exactly nail. Sure, there are absolutely elements of Skyrim that aren't amazing, there are probably mods that fix a majority of those issues nowadays.
Some competition might be FarCry and Assassin's Creed and WatchDogs, right? But in my opinion the Ubisoft cookie-cutter UI hand holding just gets boring. Cyberpunk probably comes close, but in my opinion it still lacks meaningful content. It IS a solid contender though.
There are also some great open world games out there in general. I just think personally and specifically when it comes to the open world layout, design, exploration, streamlining of all those things, Skyrim might still take the cake for me, and I think I've just forgotten that over the last 10 years or so.