Migrating Google Tag Manager during a Magento 2 upgrade works best with a structured approach: export your existing GTM container, document all dataLayer events, and use a stable extension that recreates those pushes cleanly for GA4. This reduces the risk of missing tags, broken triggers, or duplicated scripts. In the middle of planning it helps to review best way to open Magento documentation to double-check event standards and upgrade notes. Choose a module that supports versioned dataLayer schemas, works well with caching, and offers debug tools, so reimplementation stays controlled, future updates remain simple, and tracking accuracy is preserved across environments.