Explanation

Box 1: Invite User1 to collaborate with your organization as a guest.
To manage guest users of a Microsoft 365 tenant via the Admin Center portal, go through the following steps.
Navigate with your Web browser to https://admin.microsoft.com.
On the left pane, click on "Users", then click "Guest Users".
On the "Guest Users" page, to create a new guest user, click on either the "Add a guest user" link on the top of the page or click on "Go to Azure Active Directory to add guest users" link at the bottom of the page. Both of these links will take you to the Azure Active Directory portal, which is located at https://aad.portal.azure.com.
On the "New user" page in the Microsoft Azure portal, you must choose to either "Create user" or "Invite user". If you choose the "Create user" option, this will create a new user in your organization, which will have a login address with format username@tenantdomain,dot,com. If you choose the "Invite user" option, this will invite a new guest user to collaborate with your organization. The user will be emailed an email invitation which they can accept in order to begin collaborating. For the purpose of creating a guest user, you must choose the "Invite user" option.
Box 2: The Microsoft Entra admin center
Microsoft Entra admin center unites Azure AD with family of identity and access products Microsoft Entra admin center gives customers an entire toolset to secure access for everyone and everything in multicloud and multiplatform environments. The entire Microsoft Entra product family is available at this new admin center, including Azure Active Directory (Azure AD) and Microsoft Entra Permissions Management, formerly known as CloudKnox.
Starting this month, waves of customers will begin to be automatically directed to entra.microsoft.com from Microsoft 365 in place of the Azure AD admin center (aad.portal.azure.com).
Reference:
https://stefanos.cloud/kb/how-to-manage-microsoft-365-guest-users
https://m365admin.handsontek.net/microsoft-entra-admin-center-unites-azure-ad-with-family-of-identity-and-acc