Microsoft announced that the in-app notifications feature has reached General Availability (GA). This builds on the public preview announced July 2021 in Announcing public preview for in-app notifications.
In-app notifications enable a user to receive a notification while they are working within the web or mobile model-driven app. Notifications can be sent from Power Automate, app logic or web service calls allowing flexibility in where notifications are triggered.
Please refer below blog for more information –