When a user sends a sharing request to an external recipient, behind the scenes, SharePoint is triggering the creation of an Azure Business-to-Business (B2B) account in your organization's Azure Active Directory tenant. When the user receives this invitation via email, they can click on the link provided to complete their Azure account provisioning in your tenant. For example, let's say you want to create a sharing invitation for a user outside of your organization, as shown in the following screenshot:

After you click Send, you will see a new account of type – Guest – in the Azure Active Directory portal, as shown in the following screenshot:

This is the security principal in your environment that will be granted access to resources. Since it is a security principal in your environment, you can manage it in the same way you manage normal users, that is, by assigning conditional access policies or licenses.