Scp: ash: /usr/libexec/sftp-server: not found

My PC has:

-side library
ii  openssh-client                                 1:9.6p1-3ubuntu13.8                        amd64        secure shell (SSH) client, for secure access to remote machines
ii  openssh-server                                 1:9.6p1-3ubuntu13.8                        amd64        secure shell (SSH) server, for secure access from remote machines
ii  openssh-sftp-server                            1:9.6p1-3ubuntu13.8                        amd64        secure shell (SSH) sftp server module, for SFTP access from remote machines

I meant the other methioned thread.

I used the webbrowser to upgrade, so there are solutions of course. Thanks for explaining, I didn't know this. There is no problem to connect via ssh and keys.