I, unfortunately, have first hand experience here. The short version of my story is that I started out 2020 with an acid reflux diagnosis and ended 2020 laid out in bed 24/7 eating nothing but rice and potatoes with doctors shrugging over a mystery GI issue.
They finally gave me a specially designed, brand name, and expensive as hell antibiotic that specifically targets the gut microbiota. The drug and its effect is the medical equivalent of the old IT adage: "Have you tried turning it off and on again?" The idea is to rain hell down upon your gut and hope it resets to a better balanced microbiota.
So yeah, that's the current state of modern medicine when it comes to GI issues; bludgeon it to death and hope for the best. So God have mercy on this researcher attempting to identify links between the GI microbiota and other illnesses.
P.S. I was somewhat inclined to go into more details on my journey, cause finding information on GI issues is so hard, but it would be a stupidly long comment. Suffice it to say, I learned a lot about the gut, but mostly about what we don't know. For all those people with IBS-*, SIBO, and NCGI out there, you have my deepest commiserations. Science can take the FODMAP diet and shove it up its poorly understood rectum.
EDIT: I think in my revisions of this comment I forgot an important bit: the treatment seems to have worked. My symptoms are continuing to improve after the round of antibiotics. So as crude as the science may be, at least it worked.