https://info.arxiv.org/help/submit_pdf.html explains all the constraints on direct PDF publication.

If you disagree with their good reasons https://info.arxiv.org/help/faq/whytex.html to submit the TeX you might be granted an exception.

Or just publish on zenodo, without all that fuss. The reasons the ArXiv gives may be good from their point of view, but if you don’t care too much about that but have your own good reasons for not wanting to publish your source, then zenodo is a great and in many respects superior alternative, no questions asked.