Hi @Jose_Sandrone,
In addition to the authentication workflows mentioned in the documentation that @Luke shared, Token Exchange and Authorization Code Grant, we also have a new authentication workflow for custom apps created from merchant accounts, with a bit simpler workflow than both Token Exchange and Auth Code Grant.
To give a bit more context on this change, and why you are not able to see the access tokens in the admin anymore:
Moving forward all apps are created in the Dev Dashboard, including both Partner Custom and Public apps, and Merchant Custom apps.
For custom apps, you no longer get the access token directly from the dashboard/admin, you will need to use one of the existing authorization methods instead.
And here is another Shopify.dev Community Forum thread with a bit more info as well: