HUH?!?!? What is 23,800? No such thing.
Here is a quick synopsis:
30 fps: B&W video framerate (from the old days)
29.97 fps: Video framerate, currently
24 fps: film framerate (the actual sprocketed 35mm stuff)
23.976 fps (aka 23.98): film speed pulled down to video speed (that’s a whole explanation unto itself)
23.976 would be the equivalent of, and will sync to 29.97
23.976 is NOT the equivalent of, and will NOT sync to 30
So yes, 24 fps is not the same as 23.976 fps; the latter is running @ video speed, and is 1/10% slower
You need to output your video to the framerate that you are going to set Cubase to, or - set Cubase’s framerate to the framerate that you output your video to. If you op your vid @ 30 fps, set Cubase to 30 fps. If you op your vid @ 29.97 fps, set Cubase to 29.97 fps.