It specifically says you are not allowed to commercialize the engine or a derivative, so that sounds like something that is not intended to be allowed, though I feel like it might take a lawyer to decide whether or not that is technically allowed by the license.

You'd first have to make proprietary changes, which you are not allowed to release, and so there's nobody to sell those services to.

> You are free to distribute original or modified (derivative) versions of Defold

You just don't have to release the code if you do change it.

Although I'm unsure if selling services on your modified game engine, that you released the source of, counts as commercialization.