Can I load a firewall backup on a newer firewall?

In general, yes you can: See: https://support.sophos.com/support/s/article/KB-000036245?language=en_US

Hello Paola,

Thank you for contacting the Sophos Community.

If your device is XG115 or higher you shouldn't have any issue.

Take a look at the backup compatibility in this link.

https://support.sophos.com/support/s/article/KB-000036245?language=en_US

Regards,

Thanks Emmanuel !

Thanks LuCar.