Here's my problem with negative critique of time travel in the MCU:
If we agree on some time travel basic concepts, which includes a couple of variants of how it might work, nearly all the YT reviews I've seen __still__ get it wrong (I mean, I've written 1000s of words on the subject, built a timeline for Primer before most people had seen it, you know, that level of Nerd-dom, those YT-ers are late to the party ...

)
But more importantly, people are arguing time travel and attempting to use some kind of real world reference points, in a universe, where, if we consider "real world" physics, etc., then ...
Where does Hulk's extra mass come from? Is Thor's hammer creating gravimetric force to prevent being lifted? If so, when extreme force is applied it should crush the - for example - table it's sitting on. Cap's shield violates all sorts of rules of kinetic energy, rebound/elasticity/materials physics, even with the "
but Vibranium ..." explanation. I'm not talking the suspension of disbelief over, "Can you really build a tiny arc reactor or repulsor cannons?", that's a given, it's their universe, I'm talking where there's clearly violation of actual real world science that people ignore, yet, will argue over the THEORETICAL science of time travel.
It kind of misses the point, you can't have it both ways.
Talking about this subject is fun.
Thor’s hammer does not bother me because it is imbued with
worthy magic. Cap’s magically returning shield, it must be that vibrainium.
This is what Banner should have said while looking into the camera,
This is not my area of expertise, I don’t understand it, it does not make logical sense to us but in the quantum world, somehow it works. Now maybe that might be passable, but the issue is still they are using the quantum realm just to travel to a different point in time. For everything else, time flows forward as we experience it
My impression, time is a flowing river. It has been proven that time passes at different rates based on relative motion, so we know that you can travel ahead in time relative to the earth if you travel close to the speed of light. Everything beyond that is conjecture, ok fine.
So if you have the mechanism to travel back in time, once you arrive in a point back in time, and you cause a ripple, you change something that is carried forward, most likely a bunch of things (butterfly effect).
So unless a reason can be produced other than magic

if all of the Infinity Stones were taken, at that point in time the change immediately takes effect and all future time has been altered. No Infinity War, no time machine althouh a time machine might have been invented for another reason.

Bottom line they would have never gotten back to beat Thanos, because he was probably off doing other things because he could not find the stones.
And Capt America would not have had the opportunity, by virtue of being stuck in the past of putting the stones back at the exact moment they were taken. And by virtue of being stuck in the past, a whole new history would be created of them possessing the stones, and other creatures trying to find them.
Anyway for the time traveler who is relying on a time machine in the future to retrieve them, the real danger is that no one in the future is even aware that they went back in time and then there is the issue with the huge paradox of meeting yourself like Captain America did, because there is only one of you, which puts the entire ability to travel back in time doubtful.

No there are not 2 of you, so really this is a basis for declaring time travel backwards impossible
Now, one thing I like about HGWells,
The Time Machine was that the time traveler was traveling to a point in time in the distant future (not the past) effecting the future as it happened, and he traveled so far forward that besides him disappearing from the time line, the minor changes he makes when he goes back, long enough to gathers some books and tools, the changes were trivial although I acknowledge that theoretically those minor changes could have changed time enough to make him lose the future he wanted to return to. Bottom line, this did not break my suspension of disbelief.
I also like the premise in the
Sound of Thunder (movie) if I have the right story back in time, someone steps off the path accidentally, where the future is messed up and they make multiple tries to try to get back to the future they left.