Solution
Remove neovim from your home.packages set.
Explanation
The programs.neovim.enable configuration already adds that. This is true as well for any other packages you’ve enabled with a programs.* module (such as alacritty). You haven’t run into this problem before because the other modules you use are adding the same package to home.package, but the programs.neovim module doesn’t. It instead uses pkgs.wrapNeovimUnstable pkgs.neovim-unwrapped { /* config */ }, which produces something that looks like neovim but is a separate derivation and thus conflicts.
If you look at the programs.neovim module you can see this in the configuration specified for programs.neovim.finalPackage (which is what ends up in home.packages).
In general, any package you enable via a module should not be added separately to home.packages.