There is an issue in the installer that it isn’t aware of the new location we chose for this. Generating files in /usr/share/foreman-proxy is a bad practice so in our RPM packaging we moved it to /var/lib/foreman-proxy. We still need to do the same on the Debian side and make the installer aware of this. For now the workaround is to set --foreman-proxy-plugin-remote-execution-ssh-identity-dir /var/lib/foreman-proxy/.ssh. The RPM package should have moved your keys there as well.