OBS don't support decimal numbers as a recording/streaming frame rate.
There is OBS-mp that might allow decimal, but is more limited to only allow 10, 20, 29.97, 30, 48, 59.94, 60.
No 23.976 on OBS nor OBS-mp.
Custom x264 isn't going to work, OBS itself need to sent frames to x264 encoder at the right FPS timing.