I'm not even sure if Amazon sells SIM-locked phones. I don't think I've ever seen one there.
Anyway, specifically in the title of the listing you linked to it says:
Google Pixel 9a: Android Smartphone without SIM Lock
Since the English version is machine-translated, and often gets mangled, it's good to also confirm with the original:
Google Pixel 9a: Android-Smartphone ohne SIM-Lock
Seems pretty certain it's unlocked then.
Edit: Reading your question again, to be extra clear, I think no Pixel phones you buy are OEM unlocked as such on arrival. You have to go in the settings, and enable OEM Unlocking first, and to be able to do that, they have to first be connected to the Internet. Otherwise, the button is grayed out. So I understood your question as whether they can be unlocked or not if you buy from Amazon, to which I believe the answer is a yes.