Another study of Type 1 diabetes being associated with Covid:
It’s still only a correlation, but T1 diabetes is some type of autoimmune disease, where the body attacks the pancreas cells. They postulate in the discussion as to what might be happening.
While I think the vast majority – maybe all – of nutritional epidemiological studies are worthless, this is a case where (1) there is no other way to get this information and (2) the results, even though small, might be meaningful.