If the exclusive ownership of something, in order to sell it, is the primary choice driving factor of a project. Then you should just make it proprietary. Anything else would limit your margins, since someone else can just fork your project, change it and make it proprietary themselves. A dual license is sometimes used in this case as well.
I don’t exclusively own my own works anymore. Which is different than just owning your own work.
If the exclusive ownership of something, in order to sell it, is the primary choice driving factor of a project. Then you should just make it proprietary. Anything else would limit your margins, since someone else can just fork your project, change it and make it proprietary themselves. A dual license is sometimes used in this case as well.
You can sell GPL licensed software. You don’t have to publish the source code publicly online.