I recently connected Shopify to my GMC, and its showing products I have deleted 1-2 months ago as “In Stock”. They are nowhere in my Shopify or anything but seem to still show up in my GMC, even with the photos and everything.
This is a common issue if you are using the google and youtube app, my recommendation is to uninstall and re-install the app. However be carefull the issue is that the product IDs will most likely change, because the app has changed from content api to merchant api.
this is a known glitch with the sales channel app. as emmanuel mentioned, uninstalling and installing the app will reset the products. you can try that.
or you can also go ahead with a data feed solution like adnabu.