import all references of a paper into a bibtex file
There would be a quick approach if you know how to code:

Take the DOI of that publication.

Use that DOI to access the OpenCitations API. (Example here.)

From the API, extract all the DOIs that are referenced in the citing field.

Loop each referenced DOI through a DOI-to-BibTeX-converter (such as doi2bib in Python, or CrossCite)