i don't have a Prime subscription, as I found it wasn't useful to me. But for a while I did.
What I found is that on "Amazon Prime Video", almost everything I wanted to watch needed to be paid for because it wasn't part of "Amazon Prime (Video)".
It took me a long time to realise that "what you can get on Amazon Prime (Video)" and "what you can get on Amazon Prime Video" were completely unrelated things, and that I could access exactly the same things that I wanted, at the same prices, from "Amazon Prime Video" while stopping my subscription to "Amazon Prime (Video)".
Amazon's documentation and labelling from the set-top-box app did not make this especially clear.
The Expanse last seasons were a notable exception. I'd already seen the earlier seasons on Netflix a long time before, and it was very annoying to be unable to watch the second half of the story So I was delighted when I looked on Amazon, and watched them just before cancelling my Amazon Prime (Video) subscription. Now I just watch Amazon Prime Video.
It is quite possible I've got the names of these things completely wrong. I don't really pay attention, because I very rarely use Amazon's consumer services, except via set top box. (I use AWS but that's completely different.)