Citizen Kane (1941) is not considered to be an example of film noir and yet there would barely be one reel of classic film noir at all were it not for this American drama film directed by, produced by, and starring Orson Welles.
Also starring Joseph Cotten and the players of the Mercury Theatre Citizen Kane appears right at the start of the great film noir years, and was released in same year as The Maltese Falcon, High Sierra and I Wake Up Screaming — all of which are full fat noir, proving the style was already underway.
At the same time, there's a case to be made for the fact that Citizen Kane is the archetypal, primal, principal and inceptive American film noir production.
Citizen Kane is not a crime film and does not feature any murder, femmes fatales, post-war anxiety, paranoia or otherwise any saps, heels, mooks, cops, roscoes, police procedural brutality or wandering palookas astray in an alienating urban environment.