I think the idea that all grains are bad, is a misconception and an oversimplification. A common, trendy idea without much, if any, science behind it. I think the explainations for why grains are supposed to be bad are even more flaky.
In my personal experience, I developed lots of food intolerances, at first due to ME/CFS but I could still eat almost everything (some things like gluten would cause more fatigue and some foods would upset my digestion) and later my intollerances got severe when I went on a long course of antibiotics.
Over the year and a bit since my antibiotics I have improved my gut health and my gut flora has recovered a bit, and I am now able to tolerate things I couldn't before. For instance, I had toast this morning (homemade bread) and am currently drinking a coffee - both these things are new additions in the last week or two. But even when I was at my worst, I ate porridge every day (oats and oat milk) as well as rice every week.
I actually think it's possible that grains may be somewhat essential in helping restore ful gut health. But it is well worth testing out whether certain foods, including different grains, are causing you issues and trying to address that, which may involve cutting those foods out of your diet on a temporary, or permanent, basis.