Custom bibliography

Question

I tried to create a custom bibliography style using the cmd panel and latex makebst. I watched a YouTube Video and read a lot of blog entries (for example this and this) and all had the same procedure. So i did the same. But if I use my bib style i get the message, that the Citations had not be defined though i created a sources.bib file and linked it with \bibliography{sources} (sometimes in the preambel, sometimes in the document/ between \begin{document} and \end{} and even under \end{}) and in the resulting pdf question marks pop up in the places where it use \cite{}. The sources.bib file worked with BibLatex and BibTex (where i used \autocite{} but that is not defined for the custom package).

I used the \usepackage{natbib} package as it was shown in the internet but that does not make any difference. I even tried it without any packages (no natbib, no Bibtex, nothing else) which gives me exactly the same result.

My procedure was:

Open cmd panel, type latex makebst, answering all the questions, copying the .bst file in the folder of the document i want to create, defining \bibliographystyle{first_try}, where first_try is the name I gave my .bst file and linking my sources with \bibliography{sources}.

So what have i forgotten?

Example code:

\documentclass[]{scrreprt}
\usepackage{packets} %file where i load all packages but none of them are relevant or i insert  \usepackage{natbib} there
\author{-------}
\title{+++++++}
\date{October 2022}
\begin{document}
\maketitle
I want to cite here \cite{hobbit:original}
\bibliography{sources}
\bibliographystyle{first_try}
\tableofcontents
\include{first chapter}
\include{second chapter}
%\printbibliography[heading=bibintoc,title={References}] % only for BibLatex
\end{document}