This is a somewhat divisive question and topic.
The concept of Mercury in retrograde:
It refers to those times of year in which, from the vantage point of our planet Earth, the relative motion of the planet Mercury appears to be in reverse.
If your car is on the highway among other cars, and you suddenly accelerate rapidly, the cars that were next to you will appear to be moving backwards.
At that moment, those cars are “in retrograde”.
So, that’s what the phrase refers to in literal astronomical terms.
That is not the divisive part. That’s just simple observational physics.
But the concept of ‘Mercury in retrograde’ is also based in astrological symbolism.
The divisive part is astrology itself.
Astrology belongs to the category of ‘paradigms and frameworks that are often interpreted and applied superstitiously in contemporary, modern settings’.
This may or may not be news, but for about the last 400 to 500 years, the world has been living in the Scientific era. Many concepts and ideas that were popular prior to that period have been disproven or abandoned. This has largely been a good thing. It’s a big part of why most people can live past the age of 50 for example. Which is pretty cool.
Yet many of those abandoned views and concepts continue to resonate. They’re often better, for example, at addressing the human hunger for meaning.
But are they ‘true’ or ‘untrue’, and if so, how much and why?
These are not simple questions, and honestly they’re unlikely to be conclusively settled on this discussion forum.