Google does not disclose everything, and the knowledge I have is from 12 years in the industry. I merely provided you with my experience to help you understand what I know.
I have provided you with a solution to fix the shipping issue. If you are using the free shopping app, then go to Shopify > apps > click on the app > settings > set to manual shipping.
And if the shipping settings are submitted in the feed, (then you are using a different app), clear the shipping details using feed rules here: https://support.google.com/merchants/answer/7450276?hl=en
Then follow the steps below.
Then create a free shipping option following the guide here: https://support.google.com/merchants/answer/6069284?hl=en
I understand you are annoyed I’m sharing information that may mean you can’t advertise on Google Shopping. If Google decides to suspend you.
So if you like information from Google Ads experts, please ask your question here: https://support.google.com/google-ads/community?hl=en
Someone from our team will answer your questions.
If you continue to have questions, feel free to ask.
Also I think you are confused about what a Shopify Partner is. If you like to learn what a partner is, I encourage you to read this: https://help.shopify.com/en/partners/about