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 187,092 websites that are DuracellTomi Google Tag Manager for WordPress Customers. We know of 165,505 live websites using DuracellTomi Google Tag Manager for WordPress and an additional 21,587 sites that used DuracellTomi Google Tag Manager for WordPress historically and 75,047 websites in the United States.
Get a list of 187,092 websites using DuracellTomi Google Tag Manager for WordPress which includes location information, hosting data, contact details, 165,505 currently live websites and an additional 316,738 domains that redirect to sites in this list. 21,587 sites that used this technology previously and 75,047 websites in the United States currently using DuracellTomi Google Tag Manager for WordPress.