Execute (Setup):
  let g:vimtex_fold_enabled = 1

Given tex (fold: commands):
  \documentclass{article}

  \newenvironment{ccd}{%
    \begin{centered}\begin{tikzcd}}
    {\end{tikzcd}\end{centered}%
  }

  \newenvironment{ccd}
    {\begin{centered}\begin{tikzcd}}
    {\end{tikzcd}\end{centered}}

  % this should not be folded.
  \begin{document}

  \end{document}

Execute (fold: verify):
  VimtexReload
  AssertEqual foldlevel(1),  1, 'preamble start'
  AssertEqual foldlevel(3),  2, 'newenvironment start'
  AssertEqual foldlevel(6),  2, 'newenvironment end pre'
  AssertEqual foldlevel(7),  1, 'newenvironment end post'
  AssertEqual foldlevel(8),  1, 'newenvironment - not folded'
  AssertEqual foldlevel(12), 1, 'preamble end pre'
  AssertEqual foldlevel(13), 0, 'preamble end post'

Given:
Execute (Cleanup):
  unlet g:vimtex_fold_enabled