SD WAN - can only select one interface

NAT and SD-WAN are different pieces in the product. See: https://community.sophos.com/sophos-xg-firewall/f/recommended-reads/121408/routing-in-xgv18-with-sd-wan-pbr 

It interact differently with the product. 

so if i wanted a network to go out a differernt WAN, what would it be?

SD WAN or SNAT

Both. 

so for the "incoming interface" drop down, as i can only add one interface, what do you suggest to do, add multiple SD WANS for all my different LAN networks?

You do not need to select a Interface. You could simply use the Network Object instead. No need to specify it by interfaces. 

This is kinda a limitation of Sd-WAN PBR, you can only select one interface. But you can select multiple Host Object (internal Host networks) . 

ahhh great, so group all my interfaces together that i want to go out a different WAN?

Did you look at my post? There is the technical explanation of SD-WAN.

you mean this

community.sophos.com/.../sophos-xg-firewall-how-to-configure-mta-mode-with-two-wan-uplinks-on-v18

No: https://community.sophos.com/sophos-xg-firewall/f/recommended-reads/121408/routing-in-xgv18-with-sd-wan-pbr

ive read that, sorry it doesnt say anything about how to select more than one interface tho?

are you saying i can leave that as default ie "select interface"

and change "source networks" to all my network subnets i want to go out different WAN