All very dependent on the situation
Trying to clear out the gut to restore a better microbiome, oregano oil works wonders. I’ve heard LL37 can work this way too. Probably both going to be much easier on the stomach than a prescription antibiotic…
For repopulating, obviously quality probiotic foods are best. A really high end probiotic formula like Garden of Life Primal Defense is solid too.
Digestive enzymes are great, but they may make the body become reliant on them if I recall correctly. Someone please correct me if wrong.
10-20g of l glutamine as mentioned (fasted) is amazing, really helps gut lining. Zinc L Carnosine aids in this as well.
Stomach acidity being out of whack is a whole other topic that can be delved into. Things like ACV can be utilized here.
BPC is incredible for gut health, practically cured my IBS I used to have by taking 250-500mcg for a couple months a year or two back. Since then, my digestion has been top notch.
Overall though, managing stress and choosing foods you know digest well will ALWAYS be the king for digestion. Along with enough water, fiber, and properly timed meals.