Thanks Björn!

shared/home/default.nix

@@ -95,11 +95,6 @@ in {
       ])
     ];
 
-  # TODO: still detected as python :/
-  xdg.configFile."nvim/ftdetect/star.vim".text = ''
-    au BufRead,BufNewFile *.star setfiletype=python
-  '';
-
   programs = lib.mkMerge [
     {
       direnv.enable = true;

shared/home/dev.lua

@@ -1,3 +1,6 @@
 vim.api.nvim_exec([[
     set grepprg=@ripgrep@/bin/rg\ --vimgrep grepformat^=%f:%l:%c:%m
 ]], false)
+
+vim.filetype.add({
+extension = { star = 'python' }})