1- You can pull the unit from dash and inspect the electrical connector for any backed out pins not making good contact ,use a flash light to shine in the connector?
2- these nav units is a common problem on RX330 , you can try your luck on ebay for used one , or there is website that you can send them in and they rebuild it for you
3- there is a navigation ECU located in rear , i sent you a diagram location for it ,I would disconnect and inspect connector itself
4- I suggest a lexus scanner or equivalent so you can communicate with nav ecu and retrieve the fault codes, you can tell from the fault retrieved if it is the display or the nav ecu the problem
the problem will be the display or the nav ecu in rear of the wiring is good between them
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ASE Certified Technician