There's a lot of new features on the RB floor since last year, much more than I expected to be honest. Amazing work and proves once again the cost cap penalty was absolutely inconsequential in practice. Not visible from this photo, but from others it's clear they are once again giving up on raw venturi-generated downforce since their throat is again quite high (and located in the rear, like last year) whereas Ferrari and Mercedes try using lower throat, especially Ferrari.
As was said, RB is running lower than other cars, but this demonstrates they are generating downforce in a way that doesn't depend on ever-decreasing ride height for optimal performance. They reach their ride height quickly (probably also have softer suspension settings) and are then fixed at it, meaning they operate in a window with a more predictable and stable downforce coefficient, allowing them to optimise suspension for squared velocity increase as usual. On the other hand, Ferrari e.g. undoubtedly has to make "special" settings to account for an increase in coefficient (with ride height lowering at higher speeds), requiring stiffer suspension that's hurting them - amongst other things.
The only other phenomena that can generate such downforce in RB floor, now that raw venturi throat phenomena is practically out of the picture (vs competitors) is the strong front fence vortex. With so much sculpting, looks like it's generated and sustained while working very hard, with all those flicks and turns and kicks. Like last year, RB frontal part of the tunnel is very high and this allows the vortex to develop fully and possibly get energised with other geometries there.
With everything said, it does now seem like the only way to achieve both sustainable downforce and suspension settings that allow wider operating window for the car is to give up some ground effect downforce on the floor and work on other structures to claw back raw downforce, like RB does. In exchange, you get to have your cake and eat it - even at lower speeds.