.bib file generation is broken

Question

I use the springer nature latex package (here) to create a document. After a small change in the library file of my document the bibtex file generation ".bbl" seems to become broken. Before the change, everything runs smoothly. Removing manually all files (e.g. aux, bbl) I did not see no improvement. Additionally, I tested (see here) to run 1x pdflatex, 1x bibtex, 2x pdflatex to generate the file, this also failed (no proper PDF but an empty bbl). The biber function, see here and here, was tested too. Together with the springer nature document it results in a never ending loop and no document is created.

My assumption is that the error is somewhere in my system, but I do not have any idea where and how to solve it. Therefore, I created a minimal example, see below.

My system is Ubuntu 20.04.03 LTS, all packages are up to date. Furthermore, I removed and reinstalled the package texlive-full. Also, I restarted my system. As text editor I use Texstudio.

The standard error is:

Process started: bibtex "sn-article".aux

This is BibTeX, Version 0.99d (TeX Live 2019/Debian)
The top-level auxiliary file: sn-article.aux
I found no \bibstyle command---while reading file sn-article.aux
(There was 1 error message)

Process exited with error(s)

Process started: pdflatex -synctex=1 -interaction=nonstopmode "sn-article".tex

Process exited normally

The minimal example is:

\RequirePackage{filecontents}

\begin{filecontents}{sn-bibliography.bib}
@article{bib1,
    author      = "Campbell, S. L. and Gear, C. W.",
    title           = "The index of general nonlinear {D}{A}{E}{S}",
    journal     = "Numer. {M}ath.",
    volume      = "72",
    number      = "2",
    pages           = "173--196",
    year            = "1995"
}
\end{filecontents}

\documentclass[default]{sn-jnl}% Default
%\usepackage[backend=biber]{biblatex}
\begin{document}

\section{Introduction}\label{sec1}

Test text \cite{bib1}

\bibliography{sn-bibliography}

\end{document}