If you still have on-premises Active Directory you probably are synching your directory with Azure AD using the directory synchronization tool Azure AD Connect.

As you may be already aware, there is now 2 versions of Azure AD Connect: 1.x and 2.x

The 1.x version is some sort of legacy version allowing customer still running on Windows Server 2012 R2 or earlier; this version is not supported on Windows Server 2016 or later.

Well, now is a good time to start planning deploying or upgrading the server running your Azure AD Connect as the version 1.x will be retired in August 31st, 2022 because it uses SQL 2012 components.