How do I exclude one guest disk when backing up Hyper-V?

I have a Hyper-V guest that I backup using Duplicati on the Hyper-V host. The guest has one system disk that I want to backup and a secondary disk that I don’t want to backup (it’s large and contains stuff I don’t need backup of)

How can I use the exclude settings in Duplicati to acomplish this? Either exclude the whole disk or exclude everything on it, whichever is best or possible?

I actually have two guests that I need to do this on, one Windows 10 and one Debian Linux.