Can Gen4 RX350 model use the key fob to disable the proximity unlock like the ES350? It is great when u are traveling away from home.

 

The key fob on my 2017 RX works exactly the same.

 

This feature also exists on my fourth generation 2021 RX350. You're right. To shut off the key fob you depress the lock button and while it's depressed you press the unlock button twice. A small red light on the fob will blink 4 times. There are 4 advantages to doing this:
1) You prevent anyone from cloning the fob since its no longer sending a signal.
2) You don't need to put the fob in a metal box to block the fob's signals.
3) Save the fob's battery life.
4) Great to do if you ever wash your car by hand. Just turn off the fob and you never have the car do the "lock, unlock, lock" routine as you pass the sponge across the door handles.
Pressing any button on the fob wakes it back up.