When does history “begin” and when does prehistory “end”? Is there anything before prehistory? Where do most historians draw the line? Are there any debates about this topic among historians?

First, some generalizations. History is written primarily relying on textual sources, pre-history by archaeologists with spatial, scientific material analyses. The field of archaeology has often drawn on anthropological and ethnographical concepts when attempting to interpret the practices and beliefs of past societies, even though this has shifted over time too (broadly speaking, from viewing material culture as a 'cultural index' through which societies can be interpreted, to seeing it as representing social structures, and later the construction of ideology and meaning, and now a more humanistic approach to objects and people- something akin to a biographical method). Hence there are no set dates for when history begins and 'pre-history' ends, since these are highly contingent on the individual circumstances of each society.

The problem with drawing this line between history and prehistory is that this tends to disproportionately privilege literate societies whose records survive in a textual way easily interpreted by contemporary scholars. Most scholars (historians, but also anthropologists and historical archaeologists) have are now more careful in using the label of history to prevent this 'academic apartheid' (Peter Schmidt), since it often carries with the bounds of implicit racism when denying a historicity prior to literacy. There's often a teleological assumption when viewing, say, European societies (as transitioning from prehistory) into history when chronicles begin to appear- and one pernicious extrapolation would be to suggest that certain societies are therefore 'primitive' or lacking a history, in a way that severely downplays the significance of oral history and cultural memory. Rituals, oral genealogies etc. all form their own way of historicizing and remembering the past.

Thus, there has been a recent pushback, particularly in historical archaeology, in defining their focus temporally (typically after 1500 AD) in favour of looking at it as a method which incorporates both material culture and historical contextualization to provide a richer understanding of the past. After all, whether it's for 'prehistory' or 'history', reconstruction of the past is often seen as necessary to produce sociocultural explanations and causation. Likewise, the concept of prehistory is being more critically examined, particularly by scholars beyond the Western European and Anglo-American context. This is not to advocate for some radical deconstruction of the past (of course there are significant methodological differences in analyzing different societies), but rather to avoid the normative implications of labels and to prevent uncritically reproducing narratives of the past that already center the history of certain regions on emerging from contact with European societies (often through the violent, dislocative processes of slavery and warfare).