Fourier font and enumitem misbehaviour

I believe the issue must arise from the kerning between, for example, F and the subsequent period . Therefore, I prevent the kerning by typesetting the label as label={\Alph*}., with braces, so that kerning between the letter and the dot does not apply.

\documentclass[a4paper]{scrartcl}

\usepackage{enumitem}
\usepackage{fourier}

\begin{document}
\begin{enumerate}[labelindent=10pt,labelwidth=0pt,labelsep=30.5pt,leftmargin=!,itemsep=2.00pt,topsep=2.75pt,
  partopsep=2.00pt,parsep=2.00pt,label={\Alph*}.,ref=\Alph{enumi}]
    \item Do whatever.
    \item Do whatever.
    \item Do whatever.
    \item Do whatever.
    \item Do whatever.
    \item Do whatever.
\end{enumerate}
\end{document}

If you are still not happy, you can center the letter in a fixed-width \makebox, as in label={\makebox[1.6ex]{\Alph*}.}

\documentclass[a4paper]{scrartcl}

\usepackage{enumitem}
\usepackage{fourier}

\begin{document}
\begin{enumerate}[labelindent=10pt,labelwidth=0pt,labelsep=30.5pt,leftmargin=!,itemsep=2.00pt,topsep=2.75pt,
  partopsep=2.00pt,parsep=2.00pt,label={\makebox[1.6ex]{\Alph*}.},ref=\Alph{enumi}]
    \item Do whatever.
    \item Do whatever.
    \item Do whatever.
    \item Do whatever.
    \item Do whatever.
    \item Do whatever.
\end{enumerate}
\end{document}

In order to break an automatic kerning, I suggest \/, which inserts an explicit kern, so disallowing the automatic one.

\begin{enumerate}[
  labelindent=10pt,
  labelwidth=0pt,
  labelsep=30.5pt,
  leftmargin=!,
  itemsep=2.00pt,
  topsep=2.75pt,
  partopsep=2.00pt,
  parsep=2.00pt,
  label=\Alph*\/.,
  ref=\Alph{enumi}
]

I believe you should define your own environment, instead of adding all those options in the document body.

You may also want to do

\usepackage{fourier}
\usepackage{erewhon}

which chooses a newer version of Utopia for the text font, with better support for font encodings.