Hi. Is it possible to have the Google assistant UI that pixel 4 has?
Yes, you have to spoof your device to be a Pixel 4 to enable it. I was using the Pixel 4XL props from this Telegram group: t.me/PixelProps
Have a look at the screenshots for more details, like setting the correct language.
The only thing that is missing is this color bar animation saying "Hi, I'm listening..." when summoning the Assistant. This is the reason why you will initially see no feedback when saying "Hey Google", but it is working nevertheless. I could only tell that I successfully summoned Assistant by seeing the location icon comming up in the status bar.
However, I stopped doing that because the Pixel 4XL props introduced some weird problems with the display color calibration, especially with Night Light. Also the new UI did not really have a benefit for me.