Canon EOS RP Instruction Manual page 779

Movie recording stops by itself.
If the card's writing speed is slow, movie recording may stop
z
automatically. For cards that can record movies, see = 585. To find out
the card's writing speed, refer to the card manufacturer's website, etc.
If you shoot a movie for 29 min. 59 sec., the movie recording will stop
z
automatically.
The ISO speed cannot be set for movie recording.
In shooting modes other than [ M ], the ISO speed is set automatically. In
z
[ M ] mode, you can manually set the ISO speed ( = 589).
ISO 100 cannot be set or ISO speed expansion cannot be
selected during movie recording.
Check the [ISO speed range] and [Range for H ] setting under [ z :
z
k ISO speed settings].
When [ z : Highlight tone priority] is set to [Enable], the available ISO
z
speed range starts at ISO 200. Expanded ISO speed cannot be selected
even if you set an expanded range for [ISO speed range] or [Range
for H ] under [ z : k ISO speed settings]. When [ z : Highlight tone
priority] is set to [Disable] ( = 137), you can set ISO 100/125/160 or
an expanded ISO speed.
Troubleshooting
571