It wouldn't be that difficult to make computer solitaire winnable 100% of the time actually. It would mean "cheating" by moving cards around behind the scenes though

There's an assumption with computer card games that the computer shuffles the deck once just like a real card game but that doesn't have to be true on the computer if you don't want it to be

Now, any reasonable player would notice if you reshuffle the deck in solitaire, but you could swap around the face down cards without any problem. You could have just one stack of face down cards in memory and always pop from the top when a card is flipped

Edit: Maybe this wouldn't be winnable 100%, but you could certainly nudge every hand towards being winnable