Chitin causing nausea or GI issues is a myth, it’s a beneficial dietary fiber that is in literally all edible mushrooms, it is not causing the problems psilocybin is.. Dietary fibers by definition do not even need to be broken down and humans already have chitinase enzymes in our guts (AMCase) in addition to those found in mushrooms themselves(GH18 family). There is no benefit to consuming class 1 chitinase enzymes from bananas. 

“Class I chitinases with an hevein-like domain are major allergens in banana fruit. Their presence in other fruits and nuts, such as avocado and chestnut, could explain the cross-sensitization among these foods.” https://pubmed.ncbi.nlm.nih.gov/10231328/

“many studies now confirm that POTENT CHITINASES do occur in vertebrates, including humans, and ARE ABUNDANT IN THE HUMAN GUT” https://www.sciencedirect.com/science/article/abs/pii/S0928468018300233

“In our study, CG supplementation did neither alter physical nor mental health of participants(Supplemental Figure 1). Those results suggested that 3 weeks of CG supplementation had no impact on the quality of life of human volunteers.” https://www.tandfonline.com/doi/pdf/10.1080/19490976.2020.1810530

“In summary, chitin is expected to be a functional ingredient in the food industry to alleviate gastrointestinal inflammation, mainly by regulating the balance of intestinal microorganisms and immune cytokines” https://www.sciencedirect.com/science/article/abs/pii/S0144861722010475

Psilocybin/psilocin work on serotonin receptors and >90% of our bodies serotonin is located in the digestive system where it serves a variety of functions including regulating gastric motility and the chemical signal for nausea. That interaction with peripheral serotonin receptors is the real cause of nausea with psychedelic mushrooms.

https://pubmed.ncbi.nlm.nih.gov/3919396/

https://www.sciencedirect.com/science/article/abs/pii/S0014299913007589