trzes
A divinity that's capable of acting on a physical deck of cards but not on a computer program is not much of a divinity.
Well, a divinity of that sort would be at least one that respects the laws of physics. As far as I understand most of those people who do believe in devine entities would argue that divinity acts beyond our scientific knowledge (because science is assumed to be unable to detect the devinity's actions). But most of those people would admit, that even the devine doesn't plainly contradict scientific knowledge. Everyone is free to believe what they want though.
The Fool's Dog did a tremendous amount of work on the randomization function of their apps. I don't have the technical background to explain it (a mathematician probably could) but one of my takeaways was that often a randomizer is making use of a large number of presets sorts; a "true random" sort is very difficult to achieve but the Fool's Dog managed it for their apps.
FWIW, the act of shuffling is no more indeterminate than a computer random number generator. Rather, both of them rely on the kind of "indeterminacy" that rises out of "this is too complicated to keep track of."
The best pseudo random number generators in a computer are designed to be entirely unpredictable for any human as well as for any other computer. In that respect a well programmed app is surely no less effective than an person shuffling a physical deck.
But at the same time a computer hardware ist designed to be entirely determenistic. Once it has processed all the input everything else if set in stone. That's why its random number generators are called "pseudo". This is different to a human brain's hardware that operates much closer to the atomic level where the only kind of true randomness occurs (quantum fluctuations).
I guess the trick with good tarot apps is to keep processing inputs all the time by checking the state of all the sensors (movement, GPS, mircophone, light, temperature etc). This may further improve the app's unpredictability, but also leaves more backdoors for the influence of the devine (at least for those who believe it exists). So maybe there is no big difference between an app and a human in that technical sense after all.
I still prefer my physical decks.