How do I install Google Pixel Launcher on HTC U Ultra? I used to be able to use the Google Now Launcher on my old HTC U Ultra device. Now I got a new device with Android 8.0.0 and here I cannot install the program anymore. How can I fix that?

Edit: I learned, that Google Now Launcher was replaced by Google Pixel Launcher which is not available on Play Store on this phone but can be downloaded from apkmirror.com.
Google Now Launcher was Google's first public launcher, and it was shipped on Nexus phones as well as millions of other devices, which was a simpler launcher for Android Ecosystem.
The Google Now Launcher is now listed as incompatible with almost every Android device in Play store.
Google announced retirement of Google Now launcher in Feb 2017. 
The current default launcher by Google is Pixel Launcher, which released for Pixel devices. 


You can download google now launcher from apkmirror website, and try to install it. The last build available is of Dec 6, 2017 [link].


Pixel launcher is available on Play Store, but not available for every devices(mostly for pixel devices). But, you can download Pixel Launcher from this link.  


Download apk from apkmirror website which suits with your device's  android version, architecture, screen DPI. This FAQ link may help you to find right apk for your device from apkmirror website