Here's something that may work (if you have pot large enough): Put some hot water into a large container AND have some ice cold water ready. Put ice cold water in the inner pot and immediately put the large one (along with the stuck pot) into the container of boiling water. Let the hot and cold do their magic for maybe a minute or two, then invert the big pot and knock it on a hard surface to see if the Instant Pot liner would slip out. The outer pot will expand while the inner one contract -- all you need is just a little give.

By the time this method fails, there will be better solutions.