Typically, when you sell a computer you would backup all your critical (personal data) onto an external device, and .....
Created a new generic admin user and delete all previously existing user profiles and associated data, leaving only the newly created admin user for the new owner to use, at a minimum.
Laptops as well as some desktops have an OEM factory restore partition that allows you to return the computer to its' factory condition Out of Box settings clearing all personal data.
IF you did not take steps in advance of the sale to remove your profile and others then I would strongly suggest that at a minimum you log into your Microsoft Account and change the password, as well as any other accounts and associated passwords that may have been saved by Credential Manager, both Web and Windows.