SSH without password does not work on ubuntu server 22.04.2 LTS

Question

First of all, thanks for everyone's advices.

My testing environment: two ubuntu servers (abbreviate as S1, S2)

Server version: 22.04.2 LTS

My Steps for configuring ssh login without password as below:

1. install open-ssh both server and client on S1 and S2

2. check ssh from S1 to S2 within password => OK

3. generate key pair on S1

   ssh-keygen -t ed25519

4. copy public key from S1 to S2

   ssh-copy-id -i MY_ID.pub USERNAME@IP_S2

5. check the public key appended at ~/.ssh/authorized_keys on S2

6. edit the /etc/ssh/sshd_config config file on S2

   PubkeyAuthentication yes

   ChallengeResponseAuthentication no

   PasswordAuthentication no

7. edit the /etc/ssh/sshd_config.d/50-cloud-init.conf on S2

   #PasswordAuthentication yes

8. restart the sshd on S2

   sudo systemctl restart sshd

9. ssh from S1 to S2 => Fail

   Error message: Permission denied (publickey).

NOTE-1: if I markdown PasswordAuthentication no, I can be ssh from S1 to S2. However, it still has to entry password.

NOTE-2: I have been edit the relationship between hostname and IP on /etc/hosts file.

I have referred the following posts, but can not solve my situation according to them. ref: SSH without password does not work after upgrading from 18.04 to 22.04 and Unable to disable password authentication over SSH

How to fix it?

Best appreciation.