It’s a thought experiment, not an observation. The idea is that if you have infinity and it’s truly random than eventually all possibilities emerge.

The idea of infinite monkeys typing randomly on infinite typewriters is that eventually one of them would accidentally type out all the works of Shakespeare. Many more would type out parts of the works of Shakespeare. And many many many more would type random garbage.

If we imagine for a moment the multiverse is infinite and random, then every possible universe would exist somewhere in that multiverse.

It can be taken in other directions too. It’s a way of cocneptualising the implications of infinity and true randomness.