I don't use the G-code option myself, but wonder if this is a confusion due to Autodesk's latest offer. The upgrade I did earlier this week made a number of the normally paid for only modules free for a trial period, end of May from memory. I didn't notice any free facilities being withdrawn.
In case anyone's not familiar with Fusion's licence, the full core is available free to personal users, but there are a number of advanced modules only available to professional licensees. There are also a number of paid for online services. For example, a model can be rendered extra beautifully in the cloud, worth it for high-resolution marketing purposes etc, but I've never used it.
I find the sales and download part of Autodesk's website quite confusing, but it's good once the right buttons have been clicked and the software installed.
I'll fire up Fusion later and confirm G-code still works.
Dave