Site-to-site VPN

Hello Mathew,

Thank you for contacting the Sophos Community.

As long as the configurations match between the Sophos XG and the Mikrotik, the tunnel should establish, we currently don't have specific documentation for this configuration.

However, I did find a couple of community forums that might be useful for you. 

IPSEC VPN, XG and Mikrotik Router

VPN IPsec Connections Sophos XG to Mikrotik

Mikrotik and Sophos IPSec Site to Site

And also this 3rd Party Youtube Video

And you can check our KB on Troubleshooting IPsec and Most common scenarios.

Regards,