Using Vim 9.0.2103 under Linux with netrwPlugin.vim from Feb 09, 2021.
Typing
vim --clean -u ~/.viminrc
with ~/.viminrc reading
set nocompatible
let &rtp = '~/.vim/plugged/vim-vinegar/' . ',' . &rtp
then
:~/.vim/plugged/vim-vinegar/README.markdown<cr>-
shows the cursor at the first line instead of README.markdown.