Just because we can't determine why something happens doesn't mean its not predetermined. Every RNG gets its seed somehow, I don't see how we can be so sure that there is absolutely _zero_ cause for a given effect.
Bell's Theorem implies that if there is some kind of hidden variable controlling the outcome of a random quantum event like a seed, then it must work non-locally, which maybe doesn't completely rule it out, but it's really suggestive given that locality is one of the common assumptions like conservation of energy that has lead to a lot of progress in physics.
Interestingly, there is a local deterministic interpretation of quantum mechanics: the Many-Worlds Interpretation. The interpretation is considered by many to be what the Schroedinger equation by itself with nothing extra added (like wave function collapse) implies about the world. There is no objective randomness. The 10,000-foot view of it is that any random quantum event with multiple possible outcomes causes the world to branch into a separate world for each outcome. (Generally random quantum events have a continuous outcome space instead of discrete outcomes, but it's harder to talk about a continuous spectrum of "worlds". The "worlds" of MWI aren't necessarily discrete atomic things; the word "world" is more of a fuzzy label for our convenience, like the word "pile". Also, per the Schroedinger equation, there's situations where multiple histories leading to equivalent worlds can cancel out, decreasing the measure and therefore observed probability of that world occurring; that's how we could possibly know this whole splitting business is going on.)
However, a system like this would still have subjective randomness, in the sense that there's no way for you to predict the value of a random quantum event. (Say you have a device that when you press the button, it will measure radiation from a radioactive object inside it for a period of time, and then output "heads" if it measured more than the average amount and "tails" if less.) Assuming it's set up as advertised, the idea of predicting the result doesn't even make sense, because after the measurement, there will be a cluster of worlds with a version of you that sees "heads", and a cluster of worlds with a version of you that sees "tails". Predicting which one you'll be makes as much sense as predicting who you will be before you were born. (I find it interesting that no matter how deterministic of a universe you imagine, there's always the subjective randomness resulting from the indexical uncertainty in who you find yourself being. MWI extends indexical uncertainty like that to more situations.)
True, but I think this isn't a good response to the idea that determinism means you don't have control over your life. Reality having randomness doesn't give us more control over our lives. (If anything, I'd think that fact alone would mean we have less, because it means there's probably entropy getting in the way of whatever our true decision processes are.)
I really love the way this article puts the issue: https://www.lesswrong.com/posts/NEeW7eSXThPz7o4Ne/thou-art-p.... The idea that determinism takes away free will from us is inherently based on the idea that we're something outside of physics, and that physics is exclusively deciding the future instead of us. However, if you make the common assumption that our brain is a material object running within physics and producing our decisions, then there is no contradiction between deterministic physics and whatever is meant by free will.
Another way I like to think about it: If you made an AI and ran it in some closed simulation, would you expect it to care whether the simulation was completely deterministic (with all probabilistic events operating from a pre-chosen seed and a strong RNG) or had some kind of randomness? The question won't directly affect the AI's life inside the simulation either way. Wouldn't you find it weird if it did actually care and had a preference about that detail of its world, or if it thought it wasn't a true free AI if there was no randomness in its simulation? If the AI thought the world had randomness or not, and then learned the opposite, you'd find it weird if the AI restructured everything it knew about itself and the world directly based on that. If you the operator happened to toggle whether the simulation had randomness several times over its run while working on its code, and at some later point the AI was let out of the simulation, you wouldn't expect the AI to take offense at this change. There's nothing about its quality of life, decision-making abilities, or life circumstances that would be affected by the answer. It's just an implementation detail of its world that's not directly relevant to an intelligence, except in matters of modeling how the world works.