Chance: Is It Real?
You have some aspects right and others wrong. The definition of
probability is the frequency of possible outcomes of repeated random events (random in this context means that all events have an equal chance of being selected).
Think of probability as a ruler, and we are using it to measure possible outcomes, in the same way you might measure a length of string. Now, there is a true frequency of occurrences for those possible outcomes, which is every bit as objective and real as the length of the string, and, like the length of the string, we lack the ability to measure the true value. We can approximate the length of the string, but our methods and tools are not fine enough to find the true length of the sting. The same holds true with probability.
For the given possible outcomes, there is a true frequency of occurrences, which we measure and approximate with a "ruler" we call probability. The fact that those occurrences occur by contingent causation is irrelevant to that measurement, as that is not what we are measuring. We are measuring the frequency of possible outcomes, which does have a true value - even if we can only approximate it.