Disposable Qubes are not intended to be robustly anti-forensic in nature. Implementing robust anti-forensic measures in stateful hardware requires far more from the hardware layer than is on offer.

There have been and are some community efforts towards mitigations, but nothing remotely approaching what three (soon to be four) specific phone architectures provide.

Qubes OS is many wonderful things, but it is not particularly anti-forensic. If anti-forensics on PC hardware is the primary intention behind disposable VMs, there are better options.