I’m not a lawyer, but this seems illegal, they can’t retroactively change licenses, imagine Microsoft decides that starting January 1st you need to pay them 20¢ each time you open the file explorer or each time you boot windows. They can’t just decide to change their pricing strategy for an existing product that people have already agreed to. They could make it that starting from version X that would be the price, because people with games already released or in the works can keep the current terms with the downside of not being able to update the engine, or even have a page where people can contact them to tell what is their current project so that projects that started before this date are not affected. But the way it’s being done feels like it should be illegal.