@osolbakk
1. In the apply to each action above Create Item action, add Filter Array action
2. In this Filter Array, select output of master list Select action from Dynamic content
3. On the left side input box of filter array use below expression from dynamic content
item()['SAP_VENDOR_KEY']
4. On the right side input box of filter array use below expression from dynamic content
items('Apply_to_each')?['SAP_VENDOR_KEY']
5. Select equals to from dropdown

6. Then add condition action, use below expression on left input, select greater than from dropdown and on right side provide 0 value
length(body('Filter_array_2'))

7. In Yes branch of condition action, you can get the name of the vendor (the vendor name that has updated) using following expression in Compose action
body('Filter_array_2')[0]['VENDOR_NAME']

8. In No branch of condition action, you can move the Create Item action that you have currently. As the no branch of condition indicates that the Vendor with that ID doesn't exists in the master list.
Screenshot of how your whole Apply to each action will look
