For older movies, you might consider getting a Netflix DVD subscription though they've let their back catalog deteriorate. (Your library is probably also a good source.) You can also just digitally rent a la carte on Amazon or Apple. By and large, the streaming services have never been great for finding a specific film.
Unfortunately, most of that isn't available on AMC+, so what's the point?
I'd pay good money for access to movies pre-2000, plus a decent series or two that are exclusive, which IMO should be cheaper to obtain.