Struggling to do a system link on Halo 3 ODST co-op campaign with Xbox Series X and...

I've been trying to play the Halo 3 ODST co-op campaign with some family members split-screening on the Xbox One whilst I join the party using the system link. None of us use Xbox Live or Game Pass. When we try to connect to each other's party using the system link a message appears saying our connection is incompatible and we use an open NAT (both Xboxes are on the same WiFi, in the same room).

Is my Series X incompatible with the Xbox One or is it something else?

A step by step guide to resolving the issue would be much appreciated.

:)