Well it seems to me that film noir is a crime drama with German expressionist cinematography, otherwise there is not much else to distinguish them from just regular crime dramas.
There are also certain themes and tones that are common with many noirs, as well as various tropes. A quick google search would give you a better understanding than I could at the moment.
I'm not sure what counts as noir, but I saw M (1931), The Big Heat (1953), The Maltese Falcon (1941), Casablanca (1942), Kiss Me Deadly (1955), I, The Jury (1983), Against All Odds (1984), Cape Fear (1991), Double Indemnity (1944), Body Heat (1981), The Last Seduction (1994), The Skin I Live In (2011), Detour (1945), Heat (1995), To Live and Die in L.A. (1985), Seven (1995), and Night of the Hunter (1955), if all those count.
M was a German film made well before the American film noir movement (which was driven the European directors who had come to America), and it was undoubtedly a huge influence on many of the noir directors. And of course the director Fritz Lang came to America and made several film noirs, including The Big Heat.
Casablanca is not film noir. All the films you list from the 80s and 90s could at best be classified as neo-noir while The Skin I Live In is not noir. Against All Odds is a good movie but it's a remake of a much better movie, which is one of the most thoroughly noir movies ever in my opinion, Out of the Past.
In my humble opinion The Maltese Falcon and Double Indemnity would form the templates for the two basic kinds film noirs that followed, the one with a private detective (or other "good guy" as the lead) and the other branch being the average guy who is dragged into crime due to some sort of character weakness. And as I said, there's Out of the Past, which as a film noir, is perfect.
Some of the must-see neo-noirs would be Chinatown, Blade Runner, The Friends of Eddie Coyle, The Grifters, and some of the films of the Coen brothers, like Blood Simple, The Man Who Wasn't There, and Miller's Crossing, which is a gangster movie, but its basic plot premise is borrowed from Hammett's The Glass Key, and it seems to pay homage to various film noirs.