Colors changed drastically after the nvim 10.0 update
nvim 9.5
nvim 10.0
You're reporting this issue to the wrong repo. If the change was caused by an update of nvim, you gotta report it there. (I've seen similar reports for multiple colorschemes now, but idk if that breaking change was intentional or not).
In fact this repo (the original gruvbox) has not received an update to the colors or highlight groups in over 6 years (just view the commit log). Plus it's not even neovim-aware. If you want a more up-to-date gruvbox, checkout gruvbox-community or gruvbox.nvim.
edit: this was an intentional breaking change by Neovim, see https://neovim.io/doc/user/news-0.10.html
the problem isn't related to nvim, they just changed the original colorScheme, most color schemes set their own colors for everything so if nvim changes its colors i won't affect the color scheme, this is not the case for gruvbox.
example : gruvbox
tokyonight
I have this issue too. Any progress?
For any neovim users, just switch to ellisonleao/gruvbox.nvim, which is a Neovim Lua port that works just fine (It's also well-maintained)
I don't configure neovim with lua, and I found the default settings of the lua port mentioned above to be different than what I wanted. gruvbox-community worked as a drop-in replacement for me.