Currently mirrorless cameras are able to use Canon FL lenses via an adapter. This is effective for users demanding shots with character and vintage look, at the cost of image quality. However, cameras like the EOS M100, M6 and M5 with DIGIC 7 have advanced lens aberration correction tools, making it possible to shoot sharp images.
Canon released 3 'levels' of standard lenses (exc. macro). The f/1.8 lenses were small and lightweight, f/1.4 were mid-range, and the f/1.2 were professional level (top of their line). The recommended lenses for creating a filmic effect are the f/1.4, f/1.4 I, f/1.8 and f/1.8 II because they had only 6 elements.
The FL 19mm F3.5 (not the 19mm F3.5 R) was a true wide angle (short focus) lens. Its rear projected far into the mirror box on an SLR, and because of this, it could only be used on a camera with mirror lock-up (FP, FX, FT, F-1 (old), FTb, EF). It could not be used on either Pellix model.
The FL P 38mm F2.8 also projected into the mirror box. It was specially designed for the Pellix and could not be used on any other camera because the moving mirror would hit the rear of the lens. This lens had a longer lens mount index (the pin on the back or the lens at the top), that only fit the deeper cutout at the top of the Pellix's lens mount, thus making it impossible to mount this lens on any other camera.
the FL M 100mm F4 was a special purpose bellows lens. It could only be used when mounted on a bellows, such as the Bellows FL, because it lacked a focusing ring.