It is all open, bulk-downloadable sources. Here are some links.

  - arXiv: bulk on S3 (https://info.arxiv.org/help/bulk_data_s3.html)
  - PubMed Central Open Access: AWS Open Data (s3://pmc-oa-opendata).
  - bioRxiv / medRxiv: their monthly S3 dumps
  - OpenAlex: for citations, metadata, abstracts (https://developers.openalex.org/download/download-to-machine) 
  - AlphaFold — structures (https://alphafold.ebi.ac.uk/download)
  

Thanks for the question.