This plugin places the GTM container code snippets onto your wordpress website so that you do not need to add this manually.
https://wordpress.org/plugins/duracelltomi-google-tag-manager/
Widgets · WordPress Plugins
Get access to data on 222,447 websites that are DuracellTomi Google Tag Manager for WordPress Customers. We know of 175,980 live websites using DuracellTomi Google Tag Manager for WordPress and an additional 46,467 sites that used DuracellTomi Google Tag Manager for WordPress historically and 79,818 websites in the United States.
Get a list of 222,447 websites using DuracellTomi Google Tag Manager for WordPress which includes location information, hosting data, contact details, 175,980 currently live websites and an additional 194,080 domains that redirect to sites in this list. 46,467 sites that used this technology previously and 79,818 websites in the United States currently using DuracellTomi Google Tag Manager for WordPress.