If you don't need live updating output, you can just set grepprg and get results in the quickfix list with :grep[!] (or the location list with :lgrep[!]).

  if executable('rg')
    let &grepprg = 'rg --vimgrep $*'
  endif

No need for Fzf/Telescope/Denite/DDU or anything else in that case.

See:

https://neovim.io/doc/user/quickfix.html#%3Agrep

https://neovim.io/doc/user/options.html#'grepprg'