I had this problem already and Mounjaro made it worse. Aim for around 35 grams of fiber a day. I figured my daily fiber supplement was enough until the label showed that even at the max dose it gave only 5 grams. What finally worked was a step I ought to have taken way earlier than Mounjaro: fiber muffins. Each one has about 15 grams, I bake a batch weekly and eat two a day. Add other foods, mainly keto-style low carb dishes, and I now get plenty of fiber. Metamucil helps some people, but I skip it because psyllium husk clumps into a gel inside the gut and slows things down, which is how it works, and Mounjaro slows digestion too, so together they'd worsen constipation.