How do I modify each instance of setcookie?

I have an internal WordPress site that I’m trying to embed via iFrame. Currently, I’m stuck on:

Error: Cookies are blocked or not supported by your browser. You must enable cookies to use WordPress.

I have tried to add the following to my .htaccess:

<IfModule mod_headers.c>
Header set Access-Control-Allow-Origin https://parent.com
Header set X-Frame-Options ALLOWALL
Header always edit Set-Cookie (.*) "$1;Secure;SameSite=none"
</IfModule>

<IfModule LiteSpeed>
ForceSecureCookie secure same_site_none
</IfModule>

However, the cookies still appear without SameSite=None:

When I set a custom cookie:

function add_cookie( ) {
    $cookie_options = array(
        'expires' => time() + 3600,
        'path' => '/',
        'domain' => 'xxx.com', // leading dot for compatibility
        'secure' => true, // only transmit over HTTPS
        'httponly' => true, // make cookie accessible through HTTP protocol only
        'samesite' => 'None' // None || Lax || Strict
    );

    $set_cookie = setcookie( 'wp-test-cookie', 'samesite', $cookie_options );
}

add_action( "login_init", "add_cookie" );

It sets it correctly:

Any suggestions?