This formula makes a lot of assumptions based on our own evolution, but does so selectively. For example, the fact that we exist means the odds of intelligent life evolving are 100%, but this formula ignores that reality while including preconditions for intelligent life drawn from our own history, such as the idea that it requires billions of years to arise. In reality, we don't know whether our timeline is typical any more than we know the statistical significance of our own existence. We only have a sample size of one, and that's not really enough to draw any meaningful conclusions beyond the fact that life is possible.
I'm reminded of the recent discovery that the conditions on Uranus were atypical when Voyager made its flyby (https://ancillary-proxy.atarimworker.io?url=https%3A%2F%2Fwww.nytimes.com%2F2024%2F11%2F11%2Fscience%2Furanus-voyager-2-flyby.html), yet we had been assuming for decades that they were normal. That's the problem with small sample sizes.
I will caveat this by adding that having observed zero signs of intelligent life elsewhere in the observable universe lends support to the idea that the odds of intelligent life arising in any given star system are vanishingly small. Even on our own planet, all available evidence suggests that it has only happened once. However, if there is indeed randomness to the existence of life, then we would also expect clustering, so there may be galaxies and even planets with multiple forms of intelligent life, even if our own galaxy turns out to be relatively barren.