Are they really not solved? Because there are a lot of high end devices with OLED displays for a while now, eg Samsung Galaxy, iPhone X series and Huawei, and their displays haven't degraded over say 5 years from what I can tell.
Of those I've only had the iPhone X and now iPhone 12 (and will note that the iPhone X only launched in November 2017, just 3.5 years ago, and I'll never know how it lasts to 5 years anyway because my upgrade cycle remains faster than 5 years for now). But on the iPhone side of things at last, there are a host of mitigation measures both inherent to iOS and new since the LCD. The iPhone X series for example is quite aggressive by default about powering off the display. They do a decent job of it thanks to the Face ID sensors letting them have some form of attention monitoring coupled with fairly transparent quick wakeup/unlock, but it's still noticeable even now. iOS in general also has very, very little fixed chrome. Not nothing, but not much. Most of the display, as with TVs, is constantly shifting content. Even browsing the web on a tiny screen involves lots of scrolling and movement.
None of this stuff makes much if any sense in typical desktop/notebook computing. There are a lot more static UI elements present all the time, and that's a good thing with high precision mouse pointers and large screens. We count on screens to passively display information constantly, even if we're not actively interacting with them right that second. We also tend to use computers for a much longer time. I don't have a 4 year old phone. I do have a 10 year old system still in a final few months of service, and a number of 6-7 year old systems that may last longer. There are LCD displays at work even older than that still doing well.
Maybe OLED will evolve far enough to handle that acceptably as well, but I don't think you can extrapolate from phones. It's not like the industry hasn't been able to make big high resolution OLED displays for a while now. The curious dearth of them in notebooks/AIOs/standalone PC monitors points at something.
It's not particularly noticeable unless you're looking at an all-white web page or email or something, though. I switched to Apple maps navigation for a while because it avoids nearly all the above factors (fewer static elements, dark theme by default, actually turns the screen off during long stretches of "keep going straight for 40 miles") but eventually went back because I'm so used to the Google maps UX (and I stopped driving such long distances regularly).
https://www.youtube.com/watch?v=46KdDH5tSic
When you change the screen on an iPhone without pairing it correctly, the new screen will have the same burn in patterns as the old one.
I have had many oled devices for many years and I have never once seen noticeable burn in like I have never had an ssd die.
I’m not denying it exists. But the scale of the problem and the time it takes to occur make it a non issue for most use cases.