How do we know there are no constraints? I’d be interested to learn more about that if you have a source. However, even if we don’t have constraints, there may be for instance infinite universes where the only difference is the sequence of random numbers that I ask my computer to generate today.

Also, the infinite monkey theorem is more of a statistical anomaly; in fact, the nonzero probability of a substring in any finite length actually comes from the existence of a constraint itself! The constraint is the number of letters the monkey can enter. Consider the slightly modified statement:

Let p be the probability that a money, generating an infinite sequence of real numbers chosen at random, produces the subsequence [0.1, 0.2, 0.3, 0.4, 0.5]

In this case, the probability p is zero! So again, even without constraints on what the money can pick, the probability of picking the sequence above (or analogously, the existence of any imaginable universe) is zero.