No even simulation of pure quantum states scales exponentially with the number of degrees of freedom, that’s irrespective of any interpretation or invoking of n

No even simulation of pure quantum states scales exponentially with the number of degrees of freedom, that’s irrespective of any interpretation or invoking of non-unitary evolution like measurements, just pure simulation of the Schrödinger equation. If you simulate an environment to e.g. incorporate wave function collapse or measurement operations you’ll work with a master equation that also grows linearly with the complexity of the density matrix simulation.