According to:
https://github.com/kubernetes/kubernetes/blob/8cbe9e91c8b39de3dbb3b7e1eb76c586846721c5/cmd/kubeadm/app/constants/constants.go#L469-L483

// SupportedEtcdVersion lists officially supported etcd versions with corresponding Kubernetes releases
SupportedEtcdVersion = map[uint8]string{
13: "3.2.24",
14: "3.3.10",
15: "3.3.10",
16: "3.3.17-0",
17: "3.4.3-0",
18: "3.4.3-0",
19: "3.4.13-0",
20: "3.4.13-0",
21: "3.4.13-0",
22: "3.5.5-0",
23: "3.5.5-0",
24: "3.5.5-0",
25: "3.5.5-0",
}

So what problems will I face using the version 3.3.25 that currently comes with apt install etcd? Thank you