I think Dr. Fung writes about the impact on liver disease but not sure if his stuff goes into the effect on digestion. But he writes that IF can help keep you at a healthy weight, reverse fatty liver, balance hormones (especially insulin, which makes you fat) and all of those things seem to go hand in hand with liver health. I’m not a doctor but if your liver numbers are fine I don’t really see the link.
I’m not familiar with studies but recently my wife’s uncle had liver problems because of too much Advil over the years. There are two doctor s on YouTube I’ve owed that reference studies. Dr. Berg and Dr. Ken Berry. They may have something if you search their names and fasting.
Not sure on the effect on IF on something like SIBO. My understanding is that IF is generally positive for gut health with a good diet. Fasting is generally nice on the liver because your body has a break from constant insulin load that can protect against fatty liver. It sounds like they are picking at it because it is the thing that is different than normal so can be blamed. It is possible, but based on what i have read, your issues are not a common one.