My name is Yannis and I am working as a Google Analytics consultant.
I tried the plugin for one of my clients[trial period].
I found out a bug. It is related to the eventcallback. The product click is not working when Google Analytics is blocked. I think that this will affect many users.
Please check the attached screenshot.
You are correctly checking if google tag manager is undefined but in case Google Tag Manager is not blocked but Google Analytics is blocked(this is not uncommon) the product click redirection will not happen.
I think that you just need to use eventtimeout. https://www.simoahava.com/gtm-tips/use-eventtimeout-eventcallback/
Then the product click will only be blocked for 2 seconds in case Google Analytics is blocked.
Is there any plan to fix this?