Just to add that you have another customer here that would love to backup a remote system using the agent to our internal Veeam B&R server, Veeam Cloud Connect can be very expensive.
The example I have is we've setup static NAT for only port 10001 to our internal Veeam B&R server, and we have a web server in a data center with a public IP that we wish to backup to the static NAT / published IP. The repository can be seen OK but we get the same error as the OP, the backup times out.
Currently, as the above is not supported by Veeam, would a site to site / client VPN need to be used by a remote computer? Also is supporting agents connecting to an internal Veeam B&R server over static NAT a feature you will be implementing in the future?