Thank you, it is in the Checkout & system, Email marketing subscribed
Topic summary
Editing the newsletter double opt-in confirmation page (the page shown after a subscriber clicks the verification link) was the core issue.
Initial guidance pointed to Settings > Notifications (email templates), but this only affects the emails, not the confirmation page.
Latest workable approach: you can change the text shown on the confirmation page via Online Store > Themes > three dots > Edit default theme content > Checkout & system > Email marketing subscribed. Double opt-in means subscribers must confirm via email before being added to the list.
Limitations: the page’s layout/styling and adding visuals or products cannot be modified through the theme editor; the page is controlled by Shopify and not open for full customization. Some participants noted code-level changes may be the only route, but no concrete method was provided.
Outcome: text customization is possible; full visual/design changes remain unsupported. Status: partially resolved with a clear text-edit path; broader styling remains an open limitation.