State transitions are deterministic, it's only measurement that is probabilistic.

Even that is arguable. Subjective experience is probabilistic… kinda.

Do atoms decay deterministically?

As long as they are isolated, their state is a superposition of all possible states, and evolves determinsitically, with the amplitude of each of these "sub-states" evolving perfectly determinsitically. If you want to perform a measurement, you choose a possible decomposition of the superposition state and measure along that axis, and you'll get one of the values along that axis, with a probability that is the modulus of the square of the (complex) amplitude of that value.

Yes, aka. continuously. Interactions with larger systems makes it appear discontinuous.

I saw the best minds of my generation pithposting on hn.