And his point is that in most apartments in the US, you are not blocked because you're a renter.
You are wrong. Nothing in the US stops a landlord from preventing you from installing an AC and plenty do, for any reason they want.
My previous US apartment banned window mount air conditioners. I was stuck with a "mobile" AC unit that could barely handle a little humidity. Even someone in a "Historic" property in Europe that isn't allowed to touch anything would have that option as well.
In my state, they cannot. I legally have the right to install a window AC unit as long as I'm not doing any damage or violating a safety guideline.