###How to add SSH key to server   
After setting up first remote ssh connection type from your PC (not server)  
  
scp C:\Users\User.ssh*.pub user@hostname:/home/user/  
(example: C:\Users\user*\.ssh\id_ed25519.pub user@ip_address_of_the_host:/home/)  
Then enter password, after that >  
Go to your server and add your key, to ssh_authorized keys >  
cat id_ed*.pub >> ~/.ssh/authorized_keys  
And don't forget to restart ssh and sshd