UK and Israel have a deal where they can replace the software or some such.
You can fly the airframe but there is a significant reduction in capability unless you can also produce equivalent algorithms and data processing technology.
I’m not aware of any computer science breakthroughs required for the f35.
Almost by definition, any classified computer science research would be non-obvious.
I’m not sure your second point is true. The vast vast majority of classified information is very boring, or operational like frequencies of radar, etc.
Both sides know the basics, it’s what frequencies the radar comms and aircraft work at that is classified.
There’s very little “OMG this one algorithm changes everything!!”. Unless proven otherwise
The ability of someone to imagine the existence of things they are unaware of has no bearing on their existence. You could say the same of a lot of the classified materials science that underpins a lot of US weaponry hardware for which there is ample circumstantial evidence. No one is going to be talking about it on HN.