Star Wars has used Luke Skywalker to officially declare midi-chlorians unimportant. The original trilogy described the Force in purely mystical terms, but the sequel trilogy added a new pseudo-scientific dimension to it. It introduced the concept of midi-chlorians, microscopic life forms that exist within all living beings and allow the hosts to commune with the Force.
George Lucas had toyed with the idea of midi-chlorians for decades. In 1977, fresh from the success of the first Star Wars movie, Lucas began building a wider galaxy. He did this, in part, through in-universe character accounts dictated by C-3PO. "It is said that certain creatures are born with a higher awareness of the Force than humans," Threepio explained in one section on what it means to be strong in the Force. "Their brains are different; they have more midi-chlorians in their cells." Still, however long Lucas had been considering introducing midi-chlorians into Star Wars, they proved incredibly divisive. Fans objected to what they saw as an attempt to de-spiritualize the franchise.
The Disney era has done a solid job of redeeming Lucas' maligned Star Wars prequel trilogy, but so far they've completely avoided midi-chlorians. The recently-published Secrets of the Jedi seems to draw a line under them; it's supposedly written by Luke Skywalker, completed shortly before his death in Star Wars: The Last Jedi. In one section, Luke mentions midi-chlorians, and dismisses them as irrelevant.
"During the time of the Galactic Republic, the Jedi used science to explain why some of us feel the Force more strongly than others. Prospective younglings were tested by the Jedi Order for midi-chlorians - microscopic life-forms that reside in all living cells and impart the will of the Force to their hosts. Those with a higher number of midi-chlorians were able to hear the will of the Force more clearly than others. Personally, I've never been one to worry about how exactly the Force whispers to me. All that matters to me is that it still does."
In Star Wars: Episode I - The Phantom Menace, midi-chlorians served a simple purpose; they were used to give a sense of just how powerful Anakin Skywalker could be, because his midi-chlorian count was higher than anyone bar Master Yoda. The concept was referenced again in Star Wars: Episode III - Revenge of the Sith, with Palpatine referring to his master Darth Plagueis, who had been able to manipulate the midi-chlorians to create life itself. This was intended as the ultimate illustration of the Sith's perversion of the Force.
Luke Skywalker's dismissive remarks seem to speak for Lucasfilm as a whole. The studio has shown no interest in developing the idea of midi-chlorians, whether in the films themselves or in tie-ins. Like Luke, they have concluded they don't need to explore midi-chlorians and strip the Force of its mystery. It doesn't matter how the Force works; all that matters is that it does. Secrets of the Jedi appears to be the final word on this one aspect of the prequel trilogy - and, in truth, that's probably for the best.