Looks like the MCU uses the parallel universe theory version of time travel. That means time errors would create alternate universes rather than paradoxes or time line changes.
i see what you mean. Doctor Who and MCU are probably in two different universes (or imaginations) so nothing happens. But if MCU and Doctor Who collided in the film, i would have loved Endgame even more. :D
TONY STARK DISCOVERS HE CAN BUILD A TIME MACHINE; DOCTOR WHO; THE AVENGERS ARE ABLE TO GO BACK IN TIME; THEY SEE THEMSELVES IN THE PAST AND THERE ARE TWO OF THEM; THEY GO BACK TO THE PRESENT AND ARE FINE, NO SIDE EFFECTS, AND NO TROUBLE IN THE TARDIS.