I’m curious, what is your goal?
Normally an item in the marketplace exists as something that can be used by any GitHub user. Effectively, someone writes a workflow and when the workflow runs, the GitHub Action Runtime retrieves a tarball of the specified version of the action, dumps it into the environment, and then arranges to run it.
Anyone who can run a workflow can see and copy the entire content of the workflow. If you’re worried about someone stealing your sources, then putting something into the marketplace would be a bad idea as anyone could read their contents.
OTOH, by publishing to the marketplace, you aren’t responsible for paying for the CPU cycles when someone else runs your action.
For perspective, I have perhaps a dozen users of my action. They might run a couple of times an hour in each repository. That’d be a lot of cpu cycles I’d have to pay for and infrastructure I’d have to host if I wanted to self-host my action as a service. I’m much happier publishing to the marketplace and letting people use GitHub’s cpu cycles to run my action.
From an IP perspective, I rely on copyright and an open source license to “protect” my IP (that said, the license I’ve chosen is permissive, so it’s mostly imaginary).
People can publish items to the marketplace and offer them as a paid service.