K8s Control Plane Fault-tolerance | Minimum nodes and Leader Election
Official Kubernetes documentation conforms to etcd's recommendations: to achieve fault tolerance of at least one node in etcd cluster, the etcd cluster size needs to be of at least 3 nodes (odd number). The same minimum is specified in the Kubernetes documentation (min 3 nodes dedicated to etcd cluster = the same number as master nodes).
You can also empirically test it yourself using this article.