As a practical matter, studies about links between major diseases will always always be talking about correlation.
To reach 'causation' would require intentionally giving your experimental subjects Covid-19 (and in a way that didn't result in them knowing they'd had it!), and that's unlikely to pass muster with the ethics review board.
Hm, I thought other methods could be used to establish causation, such as longitudinal cohorts, RCTs, and (another randomization I'm forgetting), that wouldn't require infecting humans, but maybe I'm confusing these
To reach 'causation' would require intentionally giving your experimental subjects Covid-19 (and in a way that didn't result in them knowing they'd had it!), and that's unlikely to pass muster with the ethics review board.