I return from with good news (kind of) from the Shopify admin battleground.
I have a kind of workaround that might help some people.
Using Shopify flow and another app called flowmail.
You are able to create a flow - Order created > Check if: line items vendor is equal to “your supplier name” > Do This: Send transactional email (by specific email).
Have to set up a flow per Vendor.
If you would like to know the specific variables I used to create the email that then emails the supplier with only their products, qtys, and customer delivery address etc, ket me know and I will send across happily,
The Flowmail team are fantastic too, cant recommend them enough.
Edit: This is with only one fulfilment location set up, so Shopify doesn’t treat it as 2 orders and only calculates one weight for shipping price calculation.