I would argue that regardless of Go is low-level, for something as fundamental as a desktop environement, a lower level language makes sense.
For me I prefer higher level code and tooling wherever possible. Building this has been blazingly fast compared to previous window managers I have worked on.
exactly this.
go actually strikes a balance of being one of the few high level languages that can compile directly to binary. there are not many languages that can do that. common lisp, erlang, o'caml and maybe red are a few others that i am aware of. there are probably a few more that are less popular that i don't know.
for me high level implies at least automatic memory management and high level data types.
Does Fyne have bindings to other languages? A search for fyne python gave some hilarious AI slop from Gemini suggesting pip install fyne, but the fyne python package is something completely different and unrelated. The nice thing about GTK is it can be used from virtually any language (QT a bit less so but still a lot)