Found some time to take a better look at launch-spec floor photo from Jeddah and compare it to Monza-spec floor from Austin. Loads of changes, as we expected, I'm fairly convinced Monza floor was based on Barcelona floor with overall geometry, but the boat section and especially rear keel were changed mostly. We didn't get any useful photos of either Imola or Barcelona spec floors, so this part is just speculation
1) Area around the lower SIS tube is lower now and we know this from Barcelona photos of front turning vanes way back in June. Other than that, core geometry looks fairly similar and obviously Ferrari doesn't want to change the core flow structures on the floor
2) Front lateral boat kick is less aggressive and I suspect these lateral kicks are features that can be susceptible to asymmetric flow conditions (side wind, cornering, roll...) so keeping them moderate probably helps with flow stability across all attitudes on track
3) It's more clear now that this is where the throat of the floor roof is and this area is now lower on Monza floor
Area above 2 and 3 has also changed as a consequence, but I haven't marked it for comparison because it's not a clear difference, other than we know it has to be different
4) Rear lateral boat kick is also less aggressive now
5) As we know, diffuser keel is completely new and we've covered this topic from diffuser photos already. It's safe to say this is one of the impactful geometry changes between Barcelona and Monza floors, if not the most impactful change itself. Removing the keel kick ensures an operating window much less susceptible to ride-height changes, as these boat-kicks operate at the lowest ride height and probably induce the first separation bubble that triggers bouncing later
6) This area of diffuser, coming around rear suspension arms, seems to be changed a lot but we don't have enough details to understand how much it changes exactly. This area may have been changed with Imola or Barcelona spec