Welcome, your Pixelbook, was originally built as a chromebook, depending on its age the version of chrome OS it came with could be either Ubuntu, Gentoo or Debian 10 based,
Chrome OS is a hybrid between GNU and proprietary [google] components So assuming it still has a version of chrome these are the instructions on how it should be done
Your Chromebook automatically checks for and downloads updates when connected to Wi-Fi or Ethernet. Finish an update When your Chromebook downloads a software update, look for the "Update availab
support.google.com
[this site will also tell you how to fix your broken chrome]
Now.. If it is a pre 2018 machine it is unlikely to be updatable [chrome OS builds usually last for around 6 yrs] so you may consider changing the chrome to another OS, the one made especialy for a low spec chromebooks is
galliumos.org
ADDENDUM.... after further checking your pixelbook will take a lot of work to try and get even Galium to work [there are many known issues] you may be better off installing the latest chrome OS
Bwiz