Those are two of my favorite films. But Citizen Kane was largely unique as opposed to a precursor of a type. And Casablanca just put everything together in a package that really wasn’t that distinct from plenty of other love stories set against a WWII backdrop on the surface.
To me, both Citizen Kane and Casablanca feel pretty revolutionary in editing, compared to what was prevalent at the time. But this has intrigued me to do some '41/42 comparisons.
Appreciating "modern" before modern times requires taking the production date into context and being aware of what contemporary media was doing.
Unfortunately, the entire reason you're watching famous media decades later is because contemporary media is comparatively boring.
F.ex. How many people who have seen Citizen Kane have seen Louisiana Purchase? https://en.m.wikipedia.org/wiki/1941_in_film