Reimage Sophos Firewall support page advise to connect a monitor to the Firewall. An XGS2100 does not have a monitor port. Document does not advise what to do for this situation
https://docs.sophos.com/nsg/sophos-firewall/19.5/Help/en-us/webhelp/onlinehelp/AdministratorHelp/BackupAndFirmware/Firmware/FirmwareReimageXGFirewall/index.html#reimage-sophos-firewall_1