Just to reply to the initial question on this thread, please see the series of articles:
David Drewes, ‘The Idea of the Historical Buddha’, in Journal of the International Association of Buddhist Studies , vol.40, 2017, pp.1–25. DOI: 10.2143/JIABS.40.0.3269003. Drewes argues that we do not know anything about the historical Buddha.
Oscar von Hinüber, ‘The Buddha As a Historical Person’, in Journal of the International Association of Buddhist Studies , vol.42, 2019, pp.231–64. DOI: 10.2143/JIABS.42.0.3287480. Von Hinüber responds to Drewes, sketching out what we know from history.
Bryan Levman, ‘The Historical Buddha: Response to Drewes’, in Canadian Journal of Buddhist Studies , vol.14, 2019, pp.25–56. Levman responds to Drewes, to conclude that we know some things about the Buddha.
Alexander Wynne, ‘Did the Buddha Exist?’, in Journal of the Oxford Centre of Buddhist Studies , vol.16, 2019, pp.98–148. Wynne also responds to Drewes, and to scepticism in Buddhist Studies.