I've been using Fennel to write my Neovim configurations and it's been really nice. The setup is a bit annoying but once there it's pretty nice.
Some details about my setup (although I've moved back to lazy.nvim instead of vim.pack): https://www.jonashietala.se/blog/2025/10/29/packing_neovim_w...
Curious why you went back to lazy.nvim? I had to write some stuff to get some kind of lazy loading (now have "immediate", "vim.schedule", and "VimEnter + vim.schedule" lazy modes), plugin specs / setup functions are colocated, and using vim.packs unused `data` for config merging and it works well enough.
Also, your treesitter auto install makes a common mistake: vim file type and treesitter grammar names don't match up. IE a .tsx file has a vim filetype of `typescriptreact` while the treesitter parser is named "tsx". You'll need something like this https://github.com/nvim-lua/kickstart.nvim/blob/cfdc17be3ae1..., and there's still the note that the `vim.treesitter.language.get_lang` call isn't really doing anything, since that function returns whatever is passed in if no parser matching the name has been registered. So that check is moot.