See below for detail on learning for Az-104

Azure Learning

https://learn.microsoft.com/en-us/training/paths/az-104-administrator-prerequisites/

Azure Learning on-demand videos

https://learn.microsoft.com/en-us/shows/on-demand-instructor-led-training-series/az-104-module-1

PluralSight

https://www.pluralsight.com/paths/az-104-microsoft-azure-administrator-certification-prep

Udemy

https://learn.microsoft.com/en-us/shows/on-demand-instructor-led-training-series/az-104-module-1