If your scp fails with a Connection closed message, then add a -v to your options,

scp -p -v myfile.txt user@host:/home/user/Downloads/

to see if you get something like the following:

debug1: Sending subsystem: sftp
debug1: client_global_hostkeys_private_confirm: server used untrusted RSA signature algorithm ssh-rsa for key 0, disregarding
debug1: update_known_hosts: known hosts file /home/xmas/.ssh/known_hosts2 does not exist
Connection closed

If you see the Sending subsystem: sftp message, then there is a discrepancy between your versions of ssh. Until you get them all up to the same level, where they are using sftp, add -O (dash Oh) to your scp options to override and use the old way of transfer. You can find more information on -O in your system's man pages.

     -O      Use the original SCP protocol for file transfers instead of the
             SFTP protocol.  Forcing the use of the SCP protocol may be neces-
             sary for servers that do not implement SFTP, for backwards-com-
             patibility for particular filename wildcard patterns and for ex-
             panding paths with a '~' prefix for older SFTP servers.  This
             mode is the default.

• Originally written by Mark A. Stevens 2024/12/14
  
• man scp