If you can generate a sequence of independent fair coin flips of indefinite length (this is a big if, but hold that though), then you can effectively generate a

If you can generate a sequence of independent fair coin flips of indefinite length (this is a big if, but hold that though), then you can effectively generate a true real number uniformly from the unit interval. What you can't do is to access all of its digits all at once. But to correctly round it to a value representable in a given floating-point representation you don't need all the digits, you only need enough digits to decide whether the number falls into an interval where all reals round to the same value. As for generating independent fair coin flips of indefinite length, none of the PRNGs qualify.