These questions are inane. No, "all existing experts" did not retire. not making new plants was a decision made by politicians.
Europe has never stopped working on creating new and better nuclear reactor designs https://en.wikipedia.org/wiki/EPR_(nuclear_reactor) https://en.wikipedia.org/wiki/ITER
Iter is a research project that Europe is a part of, along with the rest of the world. That has nothing to do with building power plants, at least not anytime soon.
We haven't built a reactor in a long time. So those EPRs being built are all way behind schedule and thus costing substantially more.
You can design whatever you want. Building one is a whole different story. That's not an opinion that's just what happened at the first 2 EPRs and Hinckley point isn't going great either