You might be interested in reading this: https://en.wikipedia.org/wiki/Bell%27s_theorem

Essentially, Bell's theorem proves that quantum mechanics is not influenced by "local hidden variables". That is to say, there are not things happening which we are either unaware of or cannot measure which are influencing the outcome of quantum events. As such, certain quantum mechanical events can be said to be truly random.

The most common example of this is radioactive decay: https://en.wikipedia.org/wiki/Nuclear_decay
Another example is shot noise: https://en.wikipedia.org/wiki/Shot_noise. You can use a simple mobile phone pointed at an LED to create a true random number generator using this process: https://physicsworld.com/a/how-to-make-a-quantum-random-number-generator-from-a-mobile-phone/.

Interestingly, like bitcoin mining these processes also follow a Poisson distribution.