Guest user registration using Commerce 3
This can definitely be done, but I don't think it's possible to do it all in the same form without using a custom module to handle either creating the user programmatically and then submitting to the Commerce controller or vice versa.
Craft has support for creating a user account via a front-end form (see the User Registration Form in the Craft docs) but you can't submit to that controller and also submit to the Commerce subscriptions controller as per the standard example template at the same time.
It might be possible to achieve something close to what you're looking for by showing a user registration form first, and then set the redirect input for that form to the payment page. However, if you want to have the user logged in directly after registration but before payment in order to save the user's payment details etc., you're going to need to do some custom development work to log the user in programmatically first since the default user registration controller just creates the account but doesn't log the user in.
I've done this sort of process where the user account is created, then logged in automatically, then they enter their billing address and payment details, but that was using Commerce Pro and a multi-step registration/payment form which is a bit more complex than your use case.