I have seen a handful of desktop software apps built in Godot over the years. For example, https://bauxite.itch.io/bitmapflow is an app which I've gotten value out of built in Godot.
My favorite Godot app is Material Maker (https://www.materialmaker.org/). I downloaded it when Substance Designer was acquired by Adoboe. I'd say it actually has better usability than Designer.