I asked ChatGPT and this is what it told me:

In traditional vampire lore, the inability for vampires to cast a reflection in mirrors is often attributed to the idea that they lack a soul. This concept has been widely popularized in literature, film, and other media.

Traditional film cameras use a mirror to reflect the image onto the film (in the case of SLRs), while digital SLRs use a mirror to reflect the image onto a digital sensor. If we follow the lore strictly, a vampire wouldn't appear in these photographs.Modern smartphone cameras, as you correctly pointed out, do not use mirrors; they use digital sensors to capture images directly. If the folklore's basis for invisibility in photos is strictly tied to the presence of mirrors, then theoretically, a vampire would appear in a smartphone photograph.

However, the interpretation of vampire lore varies. Some versions might suggest that it's not just mirrors that prevent their appearance but any form of reflection or reproduction. In that case, even smartphone cameras might fail to capture them.