I've wanted to see the Canon RF 70-200mm F4 L IS USM Lens beside the Canon RF 70-200mm F2.8 L IS USM Lens, so I got around to creating a mockup today.
While both of these lenses are considerably smaller than their EF counterparts, the RF f/4 lens is considerably smaller (and lighter) than the RF f/2.8 version. Most of us prefer the smaller and lighter (and less expensive) aspects of f/4, the f/2.8 aperture's ability to transmit twice as much light to the imaging sensor and create a stronger background blur should not be overlooked.
Here are the specifications: Canon RF 70-200mm F4 L IS and RF 70-200mm F2.8 L IS USM Lens Comparison.
Order the Canon RF 70-200mm F4 L IS USM Lens from B&H | Adorama | Amazon | WEX