As you already know, Azure AD Connect (AAD Connect) is the directory synchronization tool for Azure AD and Office 365.
Azure AD Connect is getting frequently updated (about once a month), introducing new functionalities and bug fixes.
Well, starting November 2020 you will have to ensure you are running a version which is not older than 18 months onward. Indeed starting November2020, Microsoft is introducing a new depreciation policy and process for Azure AD Connect. Don’t worry your directory synchronization will not stop working but you will get Azure AD Connect Health notification to remind you to upgrade
It will start with any version older than 1.1.751.0.