Hi Jaap,
I’m also worried about this. It’s the best GTM plugin for WordPress and the developer is a really nice guy. I would be surprised if he would just abandon it. I hope he’s OK.
Have you found an alternative? I know I can just add the GTM code to the header and body but then (I assume) various data won’t be available in the data layer (add to cart, purchase value etc).
I also feel that the plugin is abandoned. I’ve been searching the support pages for several days to try to find a solution on why the add_to_cart event is not fired in our eshop but I see that the past few months no one answers the questions.. I have tried to find an alternative but didn’t succeed so far..