Fyner is an attempt to create an entirely new API for building UIs with Fyne that is more declarative. It takes some inspiration from Flutter in terms of the API design, but has a lot of its own ideas as well.
Warning: The API is very, very, very not stable. The entire thing could be restructured tomorrow with little warning if it turns out that the current design path is inherently flawed. Don't expect things to keep working until later in development.