This is why I don't belive there is scientific stagnation. New discoveries and theories are constant being made and proposed. Its only because the problems have gotten harder that progress seems slower.
In that regard I'm inclined to believe there is some sort of stagnation. Though not necessarily at the fault of the community or researchers. It could very well be a mix of what you said about problems being harder that we have, between 1900 - 2000 picked all the 'low hanging fruit' in physics, and that we now need lots of patient, 'baby step' type improvements to get to a new era where the technology is powerful enough to make big leaps again.
Kind of like how Deep Learning research stagnated due to lack of data volume and processing power.
This is my perspective, but I think it's totally up for debate and I'm keen to hear different opinions.
Although in general, I’d say it’s possible a big leap never happens again. Given that physics will ultimately be a finite set of rules, if we can explain the vast majority of phenomenon accurately, slotting the last few pieces into place might not grant us much. It will feel great for humanity to know of course, but it’s entirely plausible that the reason we have so much trouble figuring these these out is that they’re almost completely separate from the human experience. We might figure out quantum gravity, go “that’s nice”, but if it’s only relevant when there are stellar masses involved not be able to use it to change our way of life. Big changes to how humanity lives going forward could be entirely reliant on human invention/ingenuity, not us learning new facts about the universe we live in.
On the other hand, it may just be a return to the normal status quo.
So much advancement is going on in or around computing right now I think that in the future we'll sorta look back and consider that closer to science than mere engineering.