I have a 2020 RX350, purchased new in Dec-2019.
2020 is a mid-cycle refresh, and is an improvement - you can find details in a web search, and they are correct.
I'm told the suspension improvements are mild, but really good (I have never driven a 2019 or previous).
I recommend the 2020 over previous years, especially because of improvements in Infotainment system & addition of Apple CarPlay / Android Auto for 2020. Also, the radars / ultrasonic sensors have increased range and can now detect people - it works well!
Toyota & Lexus released new software in July-2019 for the powertrain / shifting issues.
It is a big improvement from what I have read.
Most 2016-2019 can get the reflash, but I saw a comment that the vehicle must have a compatible circuit board to get the software update....
My RX350 drives / shifts the same today as it did when I bought it new with 3 miles on it.
I suggest that you test-drive one gently -and- a bit spirited to see if you like it.
It does hesitate downshifting when you are creeping up a hill (such as pulling into a steep driveway).
This is a bit bothersome, but not a problem. Sometimes I manually shift to M1...easy to do.
"Sport Mode" greatly helps the transmission shift 'better' (=as expected) -> try it.
It is a rotary knob on the center console.
I suggest you try to 12.3 inch screen, with 360-degree camera.
My previous vehicle was a 2000 Honda Odyssey, so a big step-up in technology, and I use the technology every day.
Thanks to the comments / clarifying advice on the RX350 from JeffKeryk last year!