Go straight to the source -
Contact us - Home (oaic.gov.au) or in QLD
Contact us | Office of the Information Commissioner Queensland (oic.qld.gov.au)
If the device is supplied by an employer and they own the device they can install whatever apps they deem "necessary" to conduct their business, or to provide a "safe workplace." It's a grey area with surveillance in the workplace, and I suspect will require a few legal precedents to be set. Even so there may be limits.
Before COVID came along with more staff / employees / contractors working from home there were many employers (Telstra for one), and many more post COVID with surveillance software ./ apps on PC's, laptops, mobile devices, including vehicles to verify productivity, some with covert CCTV in many workplaces.
If the employee / contractor owns the device then I would not accept an "ultimatum" to install the app without seeking advice from the OAIC / OIC.