There is not any absolutely free addon for setting up Google Tag Manager in PrestaShop except purchasing a paid addon. Prestashop also doesn’t give access to Site code so we can easily include Tag Manager code but there is nonetheless an alternate way by specifically modifying the web site code https://addons.prestashop.com/pl/seo-pozycjonowanie-naturalne/30904-automatyczne-tagi-hreflang-i-tagi-kanoniczne-seo.html