Canon EOS RP Advanced User's Manual page 224

Setting the Flash Function
Slow Synchro
[ ] 1/180-30sec. auto
z
The flash sync speed is set automatically within a range of 1/180 sec. to
30 sec. to suit the scene's brightness. Slow-sync shooting is used under
some shooting conditions, in low-light locations, and shutter speed is
automatically lowered.
[ ] 1/180-1/60sec. auto
z
Prevents a slow shutter speed from being set automatically in low-light
conditions. It is effective for preventing subject blur and camera shake.
However, while the subject will be properly exposed with the flash, the
background may come out dark.
[ ] 1/180 sec. (fixed)
z
The flash sync speed is fixed at 1/180 sec. This more effectively
prevents subject blur and camera shake than with [1/180-1/60sec. auto].
However, in low light, the subject's background will come out darker than
with [1/180-1/60sec. auto].
By default, it is set to [1/180-1/60sec. auto]. To use slow-sync shooting in
o
< f > or < d > mode, set to [1/180-30sec. auto].
High-speed sync is not available in < f > or < d > mode when set to [1/180
o
sec. (fixed)].
224
You can set the flash-sync speed for flash
photography in < f > aperture-priority AE
mode or < d > Program AE mode.