Basic settings
Let’s suppose we have 2 sites in Sharepoint suggestively named "permission granted" and "permission denied".

We will now create two applications in the Microsoft Entra admin center, named AdminApp and App1.
We want AdminApp to have access to everything, while App1 will have access to site "permission granted" only.

We set Sites.FullControl.All access rights for AdminApp:

We set Sites.Selected access rights for App1:

Granting access for App1 to a specific SharePoint site
First we need to create a new HTTP request to generate an access token for AdminApp: a. Set Request method, Request URL and Request header
b. Enter settings for the body of the request
c. Send request – an access token for AdminApp is generated

Copy the siteID of our SharePoint site named "permission granted":

Create new HTTP request to grant access for App1 to SharePoint site named "permission granted": a. Set Request method, Request URL and Request header
b. Enter settings for the body of the request
c. Enter authorization settings – insert the access token obtained from the previous request
d. Send request - access for App1 to the SharePoint "permission granted" site is ready
