That's not quite true. A quantum physicist very much believes that the location of an electron exists, it's merely a probabilistic distribution along the valence of an atom. When we reject the notion of probability as a frequency (specifically a frequency of a particular event under identical starting conditions), you begin to accept probability - an intrinsic belief about the state of something - as a real, tangible thing. Do you know what the weather is tomorrow? Yes I know it: there's a 30% chance of rain.

That's not quite true, to abuse a term. But where do we begin? Do we dare ask "quod est veritas?" again?

A quantum physicist very much believes that the location of an electron exists, it's merely a probabilistic distribution along the valence of an atom. The random variable is the truth, and its characterizations achieved through observation allow us to calculate electrostatic force.

Particle physics aside, the distinction between a Frequentist and a Bayesian is always, fundamentally the interpretation of probability.

In Frequentist notation, truth is reflected in statements of probability using a subscript. A corollary is that $P_{H_0}(A \ne a) = 0$ reflects the base assumption that $a$ is the true value of $A$. It is a falsifiable statement.

Interestingly, for the Bayesian, the statement that $P(A \ne a)=0$ is a refusal to allow any further evidence to modify belief, because the likelihood for other evidence will always be multiplied by 0 with such a prior.

In summary, these two absolute statements of probability are distinguished insofar as for a frequentist truth is the beginning of science and for a Bayesian truth is the end of science. We are always in the middle.