Good day. The subscription checkbox can be moved a number of ways. This depends on the type of theme in use.
Classic Themes
If using a Classic WordPress/WooCommerce theme that uses a shortcode [woocommerce_checkout] on the Checkout page you can use our setting found on the Audience Tab of the plugin under the Opt-In checkbox position and change what is seen in the input form to the following
woocommerce_before_checkout_billing_form
Screenshot: https://loom.com/i/e21ed53be9f14bc783226ac3119e0050
This as it states will move opt-in checkbox before checkout billing form. For more options see the documentation.
Block Themes
If a Block theme is in use, one can simply edit the Checkout page directly and and drag and drop the Mailchimp block to the desired location as seen here: https://loom.com/i/c9e20824ae764c15a305fa3c1875bc61
And is it possible to move the checkbox inside the checkout_billing_form block?
It’s not currently possible to move the checkbox inside of the checkout_billing_form block. In light of your request I will raise this question to our internal development team to see if it can be added in the future. Keep in mind we here in support cannot say for sure if or when that would happen. If something changes, we will be sure to update this thread.