I left things pretty vanilla and I don't use third party apps. Many of the stock features are apps instead of ECU modules (i.e experience modes, android auto, apple carplay) which leads me to believe there is some form of ECU consolidation.
There is a clear difference in driving dynamics as you switch between the D or B mode on the gear selector as well as the experiences. Timeless feels most like a classic FWD MINI, and I prefer Core or Go Kart. There is certainly some electronic dampener manipulation of some sort.
As for personalization, it's best to link it to your MINI ID because local accounts don't allow for certain things like auto retract seats (when seatbelt disengaged), Hey MINI/Spike is also disabled without a MINI ID. Personally I disable the voice command, but leave the steering wheel button available. For the F56, MINI had more of an ICE platform that was also offered in BEV. However, for J01 and U11, it's a BEV that happens to offer an ICE variant. Now I totally get why the ICE drivers hate OS9 lag because BEV will preload OS9 and start climate control when you open the door. Not sure if that's the same for ICE.