I need slurs with five control points, as in Sibelius. This is essential when creating certain cross-staff slurs in piano music.
Can you show us an example of the kind of slur you want to achieve?
I wish I could, but I no longer have access to the Sibelius score. (I have no access to Sibelius at all because Avid doesn’t have customer support, to solve an installation problem for my recent upgrade.) But what I need to draw has an S shape.
Add a regular slur, then use the options in the properties panel to make it S shaped, then micro adjust in Engrave mode (including adding more segments if necessary). See Changing the curvature direction of slurs
You can add more then one extra segment to slurs as well.