I think it's a perfectly reasonable license. You can also use it for free with closed source projects, except embedded projects (where most of the money is), which I think is generous.

I don't think everything has to be completely free. I'd much rather they had a viable business model and actually continue existing than just fizzle out because they have no funding source. Writing a high quality GUI toolkit is an enormous task so it's not really going to happen otherwise.

As much as I'm following egui, Xylem, Dioxus, Makepad etc. and hope they succeed I'd put my money on Slint being the first to make a Rust GUI toolkit of the same quality as Qt.