Even though installing Google Tag Manager (GTM) adds a layer of complexity, it is far more flexible (and powerful) than Google Analytics (GA) alone:

GTM can be set up to track advanced analytics, like Scroll Depth, Link Clicks, & Video Playback information. GTM makes it easy to install custom tracking, like LinkedIn Insights or Facebook Pixel, without developer help. GTM makes it easier to track transaction data, like order amount, which is essential for ROI calculations for your ad campaigns.

While not difficult, it does take a little time and effort to complete. Below are the steps Volacci goes through to do a Google Tag Manager install on all our clients’ Drupal websites. 

A NOTE OF CAUTION IF YOU ALREADY HAVE GOOGLE ANALYTICS INSTALLEDExcept in very special cases,...Read the full article: Installing Google Tag Manager, Analytics, & Search Console for Drupal 9