Pretty much as the topic title says I've been playing the game a fair while now and up until the start of the week it hasn't really bothered me but its became one of those things that once its noticed I can't ignore it and its starting to annoy me, I've already done all of the "normal" stuff (switch off power saving, switch on performance optimisation) and its still pretty bad, so does anyone know any ideas or solutions?

Sadly, it's one of those things that you pretty much have to live with. I don't know why PA thinks that the pop-in is acceptable, but their engine seems to just be designed in a way that results in horrible pop-in.

It is really disappointing; this and other persistent visual issues. Black Desert looks so amazing at times, but some areas (like distant landscape or as you mentioned the pop-ins whilst moving) really detract from the overall aesthetic. PA continually laud themselves over creating 'one of the most beautiful games' but the reality is on the whole Black Desert is not this anymore. For whatever reason they are unable, or unwilling, to improve these issues, and in some circumstances have actually actively made them worse over the years. As Quelnar's said, sadly we seemingly just have to live with it.

The detailed objects are only loaded inside a fixed circle around your char. It's to reduce the data which needs to be loaded into the temp storage.
So if your char moves forward more objects need to be loaded and if you are fast you can see how they are loaded (pop ins).

You can reduce this by installing the game on a SSD or even better on a M2. If you already have installed the game on a M2, there is nothing more you can do.

And that's really the problem isn't it? People play this game with a 3080 or 3090 RTX and maybe an even better video card, the CPU, RAM, NVME can all be top of the line and we're still stuck with pop-ins. I'm not sure if it's something they consider annoying in Korea but it is annoying to experience. There's no point in having an enthusiast grade PC with gigabit internet when you have to deal with pop-ins and crazy in-game lag lol!

To completly get rid of the pop-ins, the whole map needs to be loaded when you start the game. This means every object, including every tree, stone, and blade of grass.

The problem is, no one has the machine to keep all this in their cache!

Other games reduce the pop-ins with smaller maps with and (loading) portals between each map part. and/or with less detailed environment.

The slabs of ads has become most annoying as they tell us about free login rewards.  I could understand this visual mess, if they were trying to get me to spend money on an in game ad blocker...  I better not give them any ideas.  All I can tell you, it makes me want to vomit.   

Back last year, at this time, the adverts were not too bad.  I have all or most alerts turned off in the UI settings to reduce this madness, but the players should not be subjected to visual cortex bombardment other than fighting the mobs.  How about it Kim Dae-il?  Assuming you are still incharge of your company, can you please kill the garbage ads on the screen?  Thank you.

Have fun!

That's close but not entirely right. While there is a finite limit to how many unique mesh and textures can be stored in vram / other storage, the visual pop-ins are really bad to the point that your nearby view feels broken. You don't have to travel fast, just walk and you'll see pop-ins. Meaning the same tree assets that are being rendered in front of you will pop-in a couple of meters away once you move. Also just to point it out, the blades of grass are procedurally generated like most terrain features so it comes at little render cost. But moving forward...

Game engines usually handle this in various creative ways. One of the simplest approach is to add in a fade-in/fade-out asset feature where the pop-ins and outs are less noticeable.  There is a slightly higher overhead in CPU cycles but that's not a big deal considering. Player pop-in makes sense since this is a free to play game and they can't just provide an unlimited amount of resources to support greater amount of bandwidth quota per player. The way open world maps work is that they operate on a grid called clustering. You are on the loaded cell and wherever you are looking off into the distance are also loaded (immediate cell is guaranteed load usually) and the adjacent ones aren't loaded as strongly (using load orders / poly rating).

^ That is crude and not exactly how it's done and the render engine will optimize based on where you're looking. But say Green renders everything in the cell, ren2 renders at load order within a certain range and has lower poly/textures. Ren 3 follows another load order and much lower poly/textures and ren 4 is at lowest it can go. They can define 3 types or 200 types, it's up to them. And the cell size is however big they made it. But once you do assign a cell size, then you can't go back to change it presumably without redoing everything.

In my mind, what likely happens is that the cells are small and you can just about guess the distance of them in-game using pop-ins as the clue. If we could just get an extra cell to be rendered (without other players) then we wouldn't have pop-in issues like we do right now. Then if they add fade-in and out of assets, we could really not worry so much about it being a problem.

BUT this is armchair theorycrafting. I have no idea how their game engine works and why the pop-ins are so bad. I would like to believe I have an idea but I probably don't unless they let me look at their source code. If anyone knows better, please correct me.