You may have finished off the mice yourself if and when you left the car out somewhere on a hot day.
Nothing or no one survives that. Call pest control - they are brilliant when it come to ways of eliminating rodents.
Too quote my pest guy, “the only thing that attracts rodents is food, a warm place to stay, and privacy”. In other words, they are hungry, warm blooded animals that enjoy your crumbs, but don’t enjoy your company. Sound like they found one or two of those needs in your Lexus.
As for vented seats, there is no air blowing thru the seat and the car is new. I’ll ask Lexus Support to define “The meaning of “vented” so I can troubleshoot it myself. The dealer consultant was no help by saying that it really doesn’t “vent” like you would think.
Good luck with the pest control guy - you need one...