It is a really nice and fair source-available license and there should be more of this, but a license like theirs also restricts what kind of software you can make in a rather harsh way.
Since you can't commercialise game engine products and they are defined in a broad way. You could land in legal issues. Game engine products are defined in the license as:
“Game Engine Product” shall mean software used for video game development. This includes both the content authoring software and the software used to show the created content.
IANAL, but map editors, modding tools and many other kind of tools that can be used for developing video games could be in violation of the license.
Since meaning of "commercialise" isn't being defined or narrowed in the license small creators using Patreon or the like while asking donations could be classified as a violation too.