Error: Could not start the command: bibtex.exe

Recently, I started working with natbib again and now it seems not to be working anymore.

Things that I’ve discovered:

• usually TexStudio made its own .bbl file, while currently it doesn’t
• the following error occurs: Error: Could not start the command: bibtex.exe "MAINTEX" where MAINTEX is my file name
• I tried changing my Build & View into txs:///pdflatex | txs:///bibtex | txs:///pdflatex | txs:///pdflatex
• I’m aware that the post Error: Could not start the command: […] bibtex.exe is very similar, perhaps identical

For your information, my MAINTEX file is e.g as follows:

documentclass[10pt, a4paper]{report}
usepackage[sort]{natbib}
     
begin{document}
hicite{Lee97}  

bibliographystyle{alpha}
addcontentsline{toc}{chapter}{Bibliography} 
bibliography{bib.bib}
 
end{document}

and my bib file is like

%Scriptie 2020-2021  

@book{Lee97,
    title={Riemannian Manifolds: An Introduction to Curvature},
    author={Lee, J.M.},
    isbn={9780387983226},
    lccn={97014537},
    series={Graduate Texts in Mathematics},
    url={https://books.google.nl/books?id=N8j9Gf1bQOoC},
    year={1997},
    publisher={Springer New York}
}

In addition, I’ve updated MiKTeX, and in the other post an answer given was refering to a faulty installation. Any idea what might be wrong here?