At the risk of raining on someone's parade, my efforts over more than 2 years to fit an oem reversing camera that displays on the 'big screen' have failed. N.B. my car is a 300h Executive Edition so this may not apply to upper level versions!
On the net I found a detailed account of a plug and play fitting, and removed the boot lid trim to find THE connector sitting there. Deep joy! As new cameras from Lexus were £250, and used ones weren't available, I located a company called Hushan in Taiwan who listed an OEM camera with the right part number for c.£100. I successfully negotiated the language and customs barriers; well done, me. When the camera arrived I found that the connector on this camera was completely different and would not connect to the one in the boot. DOOM!
Then I bought a complete (damaged) bootlid with camera etc. Removed the camera and plugged it in. Nothing! When the car next went in for service I asked the Service Dept. To identify the connector in the boot and explained why. Reply was that this was the connector for the camera, but a lot more electrical bits would be needed, dashboard out, possibly a new infotainment unit, so economically unviable.
Next I bought a connector adaptor from Ukraine (!) which piggybacks onto the back of the radio unit and includes a camera connector. To date I have not got this to work, and when in place, the MAP option on the menu carousel disappears! However, my son is a genius on all this sort of thing, and has the Carista software which he's had plugged into my car previously, so I will try to persuade him to have a go. However, he's very busy and lives far away.
The temporary solution that does work is a basic eBay reversing camera connected to a wireless transmitter in the boot lid. Wireless receiver is hidden under the gearshift cover, and displays on a 5" screen mounted between the seat heating switches. But I still want to get a setup that displays on the big screen!