I’ve been interested in physics since I was a kid, and read many books on the topic. The thought experiments of Einstein that led to his theories of relativity were some of the earliest topics I encountered. If you have not read of that, do so . . . I will wait.
So we come to the EPR paradox. The new field of quantum mechanics in the 1920s presented this conundrum - that particles could have entangled properties but that those properties would not become determined until a measurement event, at least according to Bohr. But upon one measurement, both particles states would be determined even if they were separated, and this determination would be instantaneous - faster than light.
The EPR paradox received further attention in the 1950s and led to the Bell’s Inequalities - describing the paradox in some detail. Bell proposed solutions to the paradox which are each a bitter pill in their own way. Some have received greater press, but there is nothing yet known to choose among them. Two that are most conspicuous are 1) a multiverse - all the outcomes exist in separate parallel universes, and 2) hard determinism - the paradox arises from quantum mechanics being predictive, but spacetime is complete and only one outcome actually exists - always has and always will.
The more I have thought on these options, the less possibility I can grasp for matters spiritual. The multiverse scenario seems ridiculously uneconomical to my admittedly-Calvinist upbringing, but if all outcomes exist, what judgement can there be for how a person lives (i.e. we live in ALL the ways we can). The hard determinism scenario is crystalline. We do not actually have any free will whatsoever - not even the free will to take advantage of being completely inculpable for our actions.
I think there may be a more mystical way of thinking of hard determinism though - a koan, if you will. We are agents of causality within a complete four-dimensional spacetime. We bring the crystalline structure of the universe into existence by virtue of our own existence in some way. <further mumbo-jumbo here>
So, we are wrestling, I think, with the phenomenon of causality. Conditions observed at time 1 are necessary to the conditions that are observed at (later) time 2. We observe the cause-effect relationship all the time - it seems to be a fundamental property of the universe. Until the 20th century, there was quite a bit of philosophical focus on determinism because the laws of physics seemed so strictly and universally applicable that physicists began to suspect a sufficiently complete observation of conditions at time 1 might predict all future conditions - even for very complex systems. Of course, we know that is not correct now; the predictive power of our theories has been constrained by such effects as quanta and chaos. But being unable to predict the outcome is not the same as the outcome being in doubt, as anyone knows who has ever watched a good detective movie. I do not know how causality is related to hard determinism - principles like quantum mechanics and chaos mathematics seem to make the path of the universe forward in time unpredictable, but they say nothing about whether we are in semi-block time (everything up until the present exists and the future does not yet exist), or block time (everything from the beginning to the end exists).
To take your example of coin flips; in the pre-20th view, a sufficient analysis of forces, positions of air molecules, etc. would give one a precise calculation of the outcome of the flip. In the post-20th view, the coin flip is unknowable until the end because not only do unmeasurably small errors in measurements make it impossible to collect sufficient data for complete analysis, but the outcomes of interactions are indeterministic. And yet, the coin lands heads or tails. So you might say (correct me if I am wrong!) that either both outcomes exist, but in different universes and when we, the observers “collapse the quantum state”, we are resolving what might have been into what is (an almost supernatural ability?), or we are perceiving a bifurcation of the universe into two separate ones; the “heads” universe and the “tails” universe. I would say that we live in block time and that our inability to predict the coin toss is a limitation on us, not the universe. The outcome of the toss is a condition in spacetime that is eternal and unchanging, and we will respond to it in the way it is.
In the matter of quotes about morality, some of which I made tongue-in-cheek and some of your own invention, regarding judgement for how one lives or doing good or bad–I’ll just say I have no desire for a moral principle in these considerations. The universe seems entirely impersonal and the only so-called spiritual reality we have is what we carry in our own thoughts. I think of the choice between multiverse and hard determinism as possibly an Occam’s Razor sort of choice. Can we explain the universe by referring to this one that we perceive directly, or do we need to refer to a vast host of others we cannot?
In regard to moral principles, I think there is no comfort to be had by those seeking such, within this discussion. If I say, the outcome is predetermined, so I cannot change it, so I will act from my own selfish desires - another can call me immoral. If you say, all the outcomes exist so make choices based on probability of good, then don’t the bad outcomes exist equally and the choice does not matter? In that case there can be no morality because just like in hard determinism there can be no choice. I think the middle road somehow exists; we are agent’s of causality within this one universe and it turns out how it does because of the things we do in it. The fact that we do them of necessity or of free choice is our own internal mental consideration.