Missing elixir highlights after installation by README

[nappex]

VIM ver. 8.2 (not self compile, .deb package from debian repo)
OS: Debian BullsEye

Reproduce the problem:

1. Install by native package manager
   git clone https://github.com/elixir-editors/vim-elixir.git ~/.vim/pack/lang-support/start/vim-elixir
2. Remove all lines in ~.vim/vimrc and keep just lines mentioned in README https://github.com/elixir-editors/vim-elixir#configuration
3. Remove all plugins and keep just vim-elixir
4. Syntax highlighting does not work

[merwan]

More information about this issue here: #562 (comment)
Reverting to commit ff7a122 fixes the problem