How to cite an item whose author only has given name, and no family name?

Question

I need to cite an item whose author has no family name, only a given name (a pseudonym). I would like the system to recognize it as a given name (because with polyglossia and french option, family names are written in smallcaps). My goal is to write given names in labels or entries in normal letters rather than smallcaps.

I use biblatex, but I guess a solution might exist for regular biblio usage?

I've tried those two things already:

@book{one,
     author={{}, William},    % Results in    [ , William]
     author={William},        % Results in    [WILLIAM]
     ...
}

but in the first case, the label is empty and the list displays the comma, and in the second case it is assumed that the name is a family name.

Do you have any idea how to proceed ?

---

\documentclass{article}


\usepackage{filecontents}

\begin{filecontents*}{\jobname.bib}
    @book{test,
      title={Le petit prince},
      author={de Saint-Exup{\'e}ry, Antoine},
      year={1943},
    }
    @book{one,
      author = {William},
      title = {First try},
      year = {2001},
    }
    @book{two,
      author = {{}, William},
      title = {Second try},
      year = {2001},
    }
\end{filecontents*}


\usepackage{polyglossia}
    \setmainlanguage{french}

\usepackage[
    backend=biber,
    style=authoryear,
    sorting=anyt,
    labelalpha,
]{biblatex}
\addbibresource{\jobname.bib}

\DeclareNameAlias{sortname}{family-given}

\begin{document}
    Look at book [\cite{one}] ! And book [\cite{two}]!
    And look at book [\cite{test}]!
    \printbibliography
\end{document}

Answer 1

Adapted from https://tex.stackexchange.com/a/429110/263192

\documentclass{article}

\begin{filecontents*}[overwrite]{\jobname.bib}
    @book{test,
      title={Le petit prince},
      author={de Saint-Exup{\'e}ry, Antoine},
      year={1943},
    }
    @book{three,
      author = {William},
      author+an = {=pseudonym},
      title = {Third try},
      year = {2022},
    }
\end{filecontents*}

\usepackage{polyglossia}
\setmainlanguage{french}

\usepackage[
    backend=biber,
    style=authoryear,
    sorting=anyt,
    labelalpha,
]{biblatex}
\addbibresource{\jobname.bib}

\renewcommand*{\mkbibnamefamily}[1]{%
  \iffieldannotation{pseudonym}
    {#1}
    {\textsc{#1}}
}
\DefineBibliographyExtras{french}{\restorecommand\mkbibnamefamily}

\DeclareNameAlias{sortname}{family-given}

\begin{document}
    [\cite{test}]
    
    [\cite{three}]
    
    \printbibliography
\end{document}