Microsoft has released new updates for Exchange Server 2016 and 2019 today. This is not a security update. The April update can be downloaded here:
The update prepares the use of the Graph API in Exchange Hybrid environments. The aim is to replace the EWS API. Microsoft writes the following:
As part of our Secure Future Initiative (SFI) we are making changes to improve the security of your Exchange hybrid configuration. One step in this journey is the separation of Exchange Server and Exchange Online identities by creating a dedicated Exchange hybrid application in Microsoft Entra ID. This is part of our efforts to deprecate the legacy Exchange Web Services (EWS) API of Exchange Online and move to Graph API calls with granular Graph API permissions. With the release of the April 2025 HUs, we are ready to start the first step of this transition.
In another blog post, Microsoft explains the changes to hybrid mode:
