Investigating hashicorp/terraform-cdk-action#42 sent me down a rabbit hole to investigate why our Marketplace page had never been updated even though we've done semi-regular GitHub releases. After doing a ton of digging, as far as I can tell, there's no way currently to automate publishing new versions to the Marketplace; a human has to manually go into the GitHub release, click "Edit", make sure the "Publish to Marketplace" box is checked, and save the changes -- only then does the new version show up on the Marketplace. There are no GH API or CLI options corresponding to this checkbox; hence the reason why it can't be automated.

As such, I don't think there's anything that can really be done in this repo, but at the very least I'd recommend putting a warning or something to this effect in the README, since it's not obvious and lots of folks might miss it.