I can't update the store via a subscription because ConnectionHandler.getConnection always returns undefined

I'm really stuck to understand how is it possible to correctly access a connection to update the store. I [posted a question on stackOverflow](https://stackoverflow.com/questions/66872369/cant-update-the-store-via-a-subscription-because-connectionhandler-getconnectio). Is it possible to reference it here ? Do you prefer I put all the code here ? Thank you in advance.