You could literally sell the unchanged Linux kernel, the GPL allows that as long as you abide by the other provisions. Convincing someone they should pay for something that you also have to provide for free might be a tad difficult but it wouldn’t be against the license
In fact, it’s more likely, since for example, you could make corporations pay for being able to use your code under a different license.
If it was MIT, they can just use it and give you fuck all.
Or, as the SME on it, you can offer paid support for it
You could literally sell the unchanged Linux kernel, the GPL allows that as long as you abide by the other provisions. Convincing someone they should pay for something that you also have to provide for free might be a tad difficult but it wouldn’t be against the license
Top-level comment:
I don’t think that commenter can sell a project under a non-GPL license if they use someone else’s GPL library in it.