The screenshots of GNvim look as if it doesn't use the code base of Gvim.
Gvim is GUI for vim (afaik its part of vim's code base). Gnvim is GUI for neovim, and is its own project.
For ppl interested in guis for nvim, i just came across https://github.com/yatli/fvim which has some nice qol improvements (compared to neovim-qt). I haven't tried it on Linux yet though
I've been using it in-terminal the last 3-4 years. I don't feel like I'm missing anything. Am I?