I was ready for flat design to die 10 years ago. It's astonishingly unintuitive, ugly, the opposite of style, and straight up anti-human. There are still abstract icons in some apps and UIs that I can't wrap my head around and I have to just click and hope I'm right. There are things that I cannot figure out whether they're interactive or not unless I just tap randomly. There are so many occasions where I can't find what I'm looking for because some goober decided contrast and color coding is a sin.
Flat design stands against every single principle of proper design. All I can hope is 40 years from now, there isn't some "retvrn to tradition" BS where a new wave of the youth decide we should return to the "cool classic style of the 2000s-2020s". Let me be an old man and die with the software around me looking beautiful.
This will happen for sure. Designs are fashions that come and go, like jeans that go from skinny to baggy and back again. I don't think anything is absolute, tastes change and people get used to just about anything, and will mainly gripe when anything changes.