My understanding of a "digital twin" is not as something that aims at simulating human biochemistry. It's rather a model that captures specific aspects, not necessarily biological ones. There's a good amount of literature on that subject, e.g. interesting meta-studies studies as [1] and [2], and more [3].

[1] https://ieeexplore.ieee.org/abstract/document/10379674

[2] https://www.nature.com/articles/s41746-024-01073-0

[3] https://scholar.google.com/scholar?q=digital+twin+health&hl=...