McLaren’s latest update at the BritishGP, at first glance, it seems has simply copied Ferrari by horizontally splitting the floorboard inlet. In reality, the change goes further.
McLaren has completely removed the upper "teeth", leaving the upper section entirely open. The remaining teeth (highlighted below in yellow) are also much longer than Ferrari’s.
On the SF26, the floorboard’s main leading edge (in blue) is thicker, which naturally shortens the teeth.

The intermediate divider (highlighted in green) works like a slat on an aircraft wing, as explained by Scarbs.