The problem is, that the “wcfmmp_store_name” is a user meta field, and not a post meta. The filter does nothing there, because the “wcfmmp_store_name” meta does not exists for the products.
I understand the issue now. While I tried to inspect the very same element it shows me as class name “wcfm_dashboard_item_title”, please see the link : https://ibb.co/z7BHRPT
I do not find this label in post meta data. Can you please guide how do I find the post meta for the vendor name ?