Used to be a Chromium extension to add more functionality to NianticLab's Wayfarer. Officially discontinued as of 9/9/21.
Check out these alternatives:
https://github.com/MrJPGames/WayFarer-Toolkit - Adds ability to add userscripts to modify behaviour
https://github.com/mariomc/WayfarerPlusUltra - Aims to be a more direct replacement for WayFarer+
Aside from that WF+ modification code can to some degree be repurposed for use with WF-Toolkit, though a understanding of Javascript, and some basic understanding of Angular are required.