The Drake equation is falsifiable. All you have to do is plug the values (which are all things that could technically be measured) into the equation, then count the number of civilizations in the Milky Way, and see if that's equal to what the equation predicted. it is possible that it's not, so the equation is falsifiable.

That it's impractical for us to actually do the experiment just means that we cannot perform the experiment and so it doesn't help us in practical terms. But it is a thing that could be done, strictly speaking.

That said, it's also a thought experiment, not a scientific postulate, so isn't "scientific" in the strict sense.