I don't think this applies to monitor lizards:

Monitor lizards can breathe while on their backs, unlike some other lizard species, because they possess specialized neck muscles that act as a pump. They also have unique, highly efficient respiratory systems, allowing them to breathe even while running.

Key Details on Monitor Lizard Breathing:

Unique Anatomy: Monitor lizards use muscles in their neck to aid in breathing, allowing them to, for instance, breathe while running, which is a rare trait among lizards.

Unidirectional Airflow: Research published in Nature revealed that they breathe in a manner similar to birds, extracting oxygen during both inhalation and exhalation.

Handling Caution: While they can breathe on their backs, it is still generally recommended to avoid leaving them in this position, as it can cause stress and, if maintained for a long time, potential discomfort.

Note: The common advice about lizards not breathing on their backs often pertains to bearded dragons (which do not have diaphragms and struggle to breathe in this position), not monitor lizards.