Hey man, fellow 2018 LX570 owner…wanted to chime in and say thank you SO much for this. Best DIY of its kind I have ever seen, and thanks for the link. My only regret is that I watched your video after purchasing, so I didn’t know to use your link to buy until I'd already bought it. My bad on that.
I've only had it installed for a few days but so far, so good. I've had a Grom VLine in my previous LX470, 2003 Land Cruiser, and IS F, and this works just as well if not better for less than half the price. Just have to deal with the goofy joystick which isn't the maker's fault. Once you get everything set up you don't have to use it much at all anyway.
For those wondering, I can double-confirm that you want dip switches 2 and 3, and the unit seems to be working well for me so far. I would assume this is true for all 2016-2021 US LX570 models.
To the guy talking about sound quality: set the EQ to flat in the CarPlay box and then adjust the factory EQ for the AUX. For whatever reason, Lexus EQ settings are source dependent, i.e. your Bluetooth EQ settings don't carry over to the AUX. I'm relatively picky myself and this seemed to fix the sound quality issues. Any reduction in sound quality vs factory bluetooth is borderline imperceptible, at least for me.
I don't have rear screens so no helpful tidbits there.
TL;DR: Thanks again, OP! Saved me $400 and your walkthrough was incredible.