Description

Microsoft has announced an update for App Service to support .NET Framework 4.8. 
Additionally, Microsoft notifies App Service users via email similar to the following:

You're receiving this email because you're running a Windows application on App Service.

To improve Azure App Service, we're updating the platform to use .NET Framework 4.8. The update will begin on July 14, 2020, and your apps will be automatically updated by September 15, 2020.

Sitecore is aware of the notice. We are researching any possible impact on Sitecore customers. Please check the article later for future updates.

UPDATE:
Microsoft has updated the announcement:

The .NET Framework 4.8 update is a non-breaking in-place upgrade on App Service. No updates are required to existing applications.

Based on this statement, no additional actions are required of Sitecore customers who host their solutions in Azure App Service.