Add the Secure flag to cookies on Shopify
Why it matters
A cookie without Secure is also sent over plain http, where anyone on the network can read it and, for a session cookie, take over the visitor's account. Secure keeps it to HTTPS connections.
Staged change. Do this in stages and check each one before the next, so a mistake does not break your site or your mail.
The fix
Not possible on Shopify. Shopify sets the storefront's own cookies and stores cannot change their attributes. If the cookie belongs to an installed app, ask the app's developer to fix it or remove the app.
Related
Scan your domain to see whether this applies to you.