We can see that "account optional" is available on Paypal's sketch:
Yet testing in the sandbox the option does not appear:
Is that due to the sandbox environment or is "account optional" feature not available for Suscriptions ?
Thank you for your support.
Edit: It also appear here that subscription should support credit card:
Unfortunately, no. Guest Checkout is not available with PayPal Subscriptions.
If you want to manage recurring profiles with direct credit cards you'll need to add PayPal Pro w/ Recurring Payments. Then you can build those types of subscriptions with a custom checkout and the APIs (or configure it in a platform/plugin that integrates it for you.)