In I3C system design, when selecting switches or multiplexers, the impact of Rds(on) on the signal must be considered: a low value can reduce voltage drop and power consumption, but the load effect of the on-capacitance (e.g., 1.5pF–15pF) on high-speed signals must be balanced; if "up" refers to "rising" or "maximum value," it may indicate the upper limit of Rds(on) . It is recommended to refer to the specific device's datasheet for accurate parameters.

This blog Based on the Tower I3C Host Adapter Pro+ test chip RDSON UP： 

Based on the Tower I3C Host Adapter Pro+ test chip RDSON (2)