Anyway, if you take the "collapse" interpretation of QM, that's a different mathematical theory, not merely a different interpretation pf the same maths.

Good catch.

Seriously, is there anyone left who actually believes in collapse any more?

Roger Penrose, at least (and he believes it for physical reasons, not because of his philosophy of mind).

Collapse actually looks better to me than anything else that's not MWI, though I haven't studied the issue in much depth – I don't understand what any interpretations besides MWI, collapse, and Bohm/hidden-variables are even saying ontologically, and Bohm has serious zombie problems.