Have you ever encountered a hand that you couldn't fold, I have encountered it many times, how did you deal with it?
It depends on what you mean by "unfoldable". Some
hands are indeed unfoldable by GTO, like aces or kings preflop, most of the flush draws on the flop or good flushes or strong top pairs on normal boards. In these instances you just don't fold them (unless you are facing an opponent that deviates heavily from optimal play) and if you lose - you just lose. It just has to happen occasionally, while you want to remain profitable and unexploitable.
If you just have a hand that looks good but you know it is too weak in this particular spot, you just have to learn how to fold them and abandon any hope for a good runout, usually reminding yourself that if you played this particular spot 100 times and didn't fold this hand, you would be losing money in the long term, because the good runouts are too rare to be profitable, helps.