I think this is mostly a problem of finding good tools for your workflow. Admittedly, there are fewer of them in the space of embedded development than for the usual "apps", but there are some. Besides the already mentioned LVGL [1] for the actual GUI you'll need a proper build tool that can handle all that conversion stuff OP's talking about reliably. I can only recommend Bob [2] here. Unfortunately, it's very unknown but brings everything you need for embedded development (w/ or w/o GUI, higher-level stuff like custom Linux images, too). Using it for years professionally and for personal projects and will never look back.
[1] https://lvgl.io [2] https://bobbuildtool.dev