Cluster-Log says "ERROR 1676: THE NODE WILL BE QUARANTINED UNTIL...." and on Nodes one Node is on quarantined.

Execute Windows Power-Shell as administrator on each node:

Import-Module FailoverClusters
Start-ClusterNode –ClearQuarantine

The status should get to "joining", that takes a moment. Of course the reason why the node was quarantined should be solved before.