Since the UI isn't behaving, you can disable this through the Metadata API with the EmailIntegrationSettings metadata type.
The field you're interested in is
enableContactAndEventSync. This'll return
true assuming Lightning sync is actually activated and preventing you from activating Einstein Activity Capture.
Within VS Code (or whichever deployment means you'd like), retrieve with the following package.xml
<?xml version="1.0" encoding="UTF-8"?>
This'll create a
Settings folder wtihin your project (if you've never pulled anything in before).
false within the
EmailIntegrationSettings file, re-deploy, and this should deactivate Lightning Sync. Thus, allowing you to go through the EAC setup within the UI.
Setup --> Outlook Integration & Sync, are you able to turn off lightning sync?
EmailIntegrationSettingsin the Metadata API. You can retrieve (using workbench or VS code) with the package.xml identified here. I presume
trueon retrieve. Change that to
enableContactAndEventSyncwas true. Einstein Activity Capture now works. Thank you. If you'd like to post your answer, I'd be happy to accept.