From the riverctl.1 man page:
*hide-cursor* *timeout* _timeout_
Hide the cursor if it wasn't moved in the last _timeout_
milliseconds until it is moved again.
The default value is 0, which disables automatically hiding the
cursor. Show the cursor again on any movement.
*hide-cursor* *when-typing* *enabled*|*disabled*
Hide the cursor when pressing any non-modifier key. Show the cursor
again on any movement.