The "computers" in a B-29 were not what we call "computers" today, so it's best not to compare them, as they're apples and oranges.
But "assisted aiming devices" have been in planes of all types sense WW2, and actual computerized versions have been included (in the modern sense of the word) since the ‘70s, with the advancements keeping track with consumer computer devices. What those advancements are will not be available for public consumption, for rather obvious security reasons. But they are very much there.
As for flying a craft in combat, computers might be up to the task, but think about how hard it's been to build a reliable self-driving car— and a car is not in combat, and operates within a highly restricted environment along delineated and designated paths, with its only movement operating on a single plane. An aircraft (or a spacecraft) operates in a much broader area of movement along three axis— x, y AND z— and that's no small complication. Throw in combat, with multiple sources of input that have to analyzed and compensated for, and things get really, really interesting for the computer programmer to devise bug-free software to handle… and it had better BE bug-free or the wrong people are gonna die.
So, having said that, computers, like humans, operate according to input received. Spook the input, and the computer will "make mistakes", same as a person will. If you know how the computer receives its input, you could possibly find ways to send false information or deny information via that input, which could be anything from laser strikes against targeting systems to EMP attacks.
EMP attacks are great against computers, and the more sophisticated the chip technology, the more vulnerable it is to an EMP attack, and thus the more shielding it will require. Shielding=mass, which is the bane of all flight— aerial or in space— so you wind up with guesstimates of what you need versus what mass you can trim by leaving something off.
However, an EMP attack requires a LOT of power, and a focused EMP strike, as a fighting craft might use, is probably not something in the offing in the near future, even a future like the Expanse.
Also, keep in mind that any deceptive signaling thrown out by a craft is also necessarily a directional signal if interpreted in another way— for example, if a craft could send out some sort of "spoof" radar signal, that same spoof signal has to originate from the craft, which means that if the deception is spotted, the sending craft WILL be spotted. (Not unlike active sonar— yes, it gives you more precise info than passive sonar, but it also tells the enemy exactly where you are.)
So, might it be possible to spoof computer-aimed guns? Yes. But that doesn't mean it's easy.
In any case in any entertainment media, devices function according to the dramatic needs of the scene. We'd much rather see Luke and Han whirling about in turret chairs blasting at TIE fighters, than Han just pushing a button in the cockpit and letting unseen computers do all the work. Best to just sit back and enjoy the show than question how or why something does or doesn't work.
