I think the information here https://docs.microsoft.com/en-us/windows-server/storage/storage-spaces/understand-quorum#dynamic-quorum-behavior (scroll down to 'two nodes without a witness) will help with your question?
I know that when I ran a cluster on Windows Server 2012 and Sql Standard 2016 the cluster would sometimes go offline when we restarted a host. I added a witness and the problem stopped. In retrospect I suspect it depended on whether the remaining node had a vote at the point of restart but I didn't know about dynamic votes at the time. I saw advice to add a witness to resolve quorum issues and, having followed that, the problem stopped so I didn't have time to investigate further.