The ssh connection from the remote server will only be done by passphrase provided that:

• the administrator of the remote server has created an account for you.
• your public key is saved in the /home/<username>/.ssh/authorized_keys remote server.
• your private key is installed in /home/<username>/.ssh your machine.

Your machine is a Unix system (Ubuntu, Debian, RedHat, freebsd, Mac …).
For Macs, the home directory is /Users/<username>.
Open a terminal on your machine (not from the remote server).
Your session <username> (no root , no sudo).
mkdir /home/<username>/.ssh
If you already have in /home/<username>/.ssh the id_rsa and id_rsa.pub files,
I advise you to make a copy.
ssh-keygen -t rsa  -b 4096 -C <username>@<domain>

Enter file in which to save the key (/home/teacher/.ssh/id_rsa):  
Enter passphrase (empty for no passphrase): Mag6@ndm&re  

You must not forget your passphrase.
ls –la /home/<username>/.ssh
id_rsa —> private.
id_rsa.pub —> public.

Copy the contents of your public key to the /home/<username>/.ssh/authorized_keys
remote server file authorizing the ssh connection.
This command makes it easier for you to transfer the copy.
ssh-copy-id -i ~/.ssh/id_rsa.pub <username>@<ipaddress remote server>

On the remote server, check if the public key is present.
cat /home/<username>/.ssh/authorized_keys

Remote server root session.
chmod 700 /home/<username>/.ssh
chmod 600 /home/<username>/.ssh/authorized_keys

Session <username>of your machine:
chmod 700 /home/<username>/.ssh
chmod 600 /home/<username>/.ssh/*

Keep copies of your public and private keys in a safe and not on your machine.

Root session of the remote machine:
Configuration of /etc/ssh/sshd_config on the remote machine.
vi /etc/ssh/sshd_config

#modify or add  
Port 22  
StrictModes yes  
PermitRootLogin no  
AllowUsers <username>  
PubkeyAuthentication yes  
AuthorizedKeysFile      .ssh/authorized_keys  
PasswordAuthentication no  
PermitEmptyPasswords no  

Configuring /etc/sshd_config.d/50-redhat.conf.
vi /etc/ssh/sshd_config.d/50-redhat.conf

ChallengeResponseAuthentication no  
GSSAPIAuthentication yes  
GSSAPICleanupCredentials no  
X11Forwarding yes  
UsePAM yes  
PrintMotd no  

Restart the ssh service.
systemctl restart sshd

To access the remote server: ssh <username>@<serveur distant>.
Passphrase password <obligatoire>.

Open a terminal on your machine (not from the remote server).
Your session (no root , no sudo).

ssh-keygen -o -a 256 -t ed25519 -C <username>@<domain>
id_ed25519 —> private.
id_ed25519.pub —> public.

Repeat the same procedure (chapter 8.3) to export the key to the /home/<username>/.ssh/authorized_keys the remote machine.
ssh-copy-id -i ~/.ssh/id_ed25519.pub <username>@<ipaddress remote server>

The connection may be rejected and the solution is to empty the content /home/<username>/.ssh/known_hosts.
> /home/<username>/.ssh/known_hosts

The easiest solution.

• You have a private and public key.
• On Windows, download PUTTYgen and Putty-installer from https://www.putty.org/.
• Open PUTTYgen —> conversion —> import your private key.
• Save the private key in ppk format.
• Launch Putty. Go to Connection, SSH, Auth and Credentials.
• Put only the private key in ppk format.

If you don't have a private key.
Putty can create it, but it will take some patience to format the public key into an acceptable format.
https://www.tutos.eu/3194 gives you the procedure.

Tip: start your machine with a “live almalinux” bootable key and create your keys.