Gmail considers several factors before surfacing the one-click unsubscribe link in the email client, even when the one-click unsubscribe headers are present in the email. Here's a community thread from Google where this has been discussed: List-Unsubscribe header not providing the option to unsubscribe.
If you've turned on the feature switch, all the future emails sent from the system includes the one-click unsubscribe headers. As long as the email contains the headers as per the specification, you can be rest assured that you're complying with Google’s guidelines. To verify this, you can download the message or select “Show Original” in the menu item of the message to verify that the headers are present.
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Dengliang Li
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