IP is property

I was surprised to see at a different post here that intellectual property is not generally considered property in libertarianism and supposedly shouldn’t be protected as such. Why is that?

Let’s say I run a pharmaceutical company and spend 1B USD (not a stretch) developing a new drug. If there is no IP, how do I recoup my costs, if my competitor can just take the compound I developed and make their own drug way cheaper?

This would freeze the field preventing any innovation, as noone would be willing to pay for it. This is the same in other fields, but pharmaceuticals happen to be my area of expertise.

Innovation requires IP. Not necessarily for as long as it is today, that is up to debate, but IP itself is crucial.