What has been learned is that the new third generation pressurised water reactor design was more complicated design than initial thought, as recognized by the Électricité de France. The first operational EPR unit started commercial operation in December 2018.
The gen 3 design is, depending on how you view it, 3 years old. It was found to be too expensive and too complex.
There exist new version of gen 3 reactors and there are design for gen 4 reactors, both claiming to solve many of the issues of the old gen 3 reactors.
And yet as I understand it, France is looking at starting 6 more of the EPR design. Though we don't know specifics, that's the only thing that seems possible to build at the moment, unless you are saying EDF has designs for newer versions, which j have not heard about.
According to wikipedia (and I assume the linked source), the 6 new EPR will be done under the newer version called EPR 2. Great naming schemes and all.
Those 6 new one was the news from 2020. The one we see in the article is unspecified and could be a reference to the 6 EPR 2 or something else. Same is true for the 150 Chinese plants being planned.
The biggest fault in the old EPR design process seem to be the mid-construct patch that occurred in 2012 as a result of the Fukushima accident. Other issues seems to be related to goals like "world’s highest-output nuclear plant". They decided to use rather exotic form of steel, within the upper limit of what can be created. Given the decision of making the highest-output nuclear plants, and there are only a few places in the world that can create and work the kind of steel that the design require, the budget did not work. In addition, the exotic nature of the material makes it difficult to weld correctly.
The open questions I see is if EPR 2 also require similar exotic materials, if the exotic materials has improved in availability and price, and if the experience in welding it has improved to the point where fewer mistakes are done. It is also possible that by not trying to achieve new world records in plant size and output, the budget might be more reasonable. The world largest and highest wind turbine might be a nice research goal, but building one at the limit of current material would not be my first choice if costs were a priority.
At the start of construction, Hinkley Point C is estimating €8.1/W. This is still four times the initial estimates cost for Flamanville 3, €2/W. But it's a bit less than the current estimated cost of Flamanville 3, €11.5/W.
However this is all assuming that Hinkley Point C stays in budget and on schedule, which would be a strange assumption to make given recent history.
So I'm not sure anything is being learned, or construction capability is increasing. Which is a shame, because that area of the world is the area with the strongest need for nuclear. The rest of the world will get by fine without it. And for that matter, it's likely that Northern Europe can build enough wind and storage to get around their need for nuclear. But it all would have been a lot easier if the nuclear industry was anywhere close to delivering on its lofty promises.
What has been learned at Flamanville that could be transferred elsewhere?