Whether you can deduct a loss all boils down to whether you actually owned an asset. For example, if you actually owned cryptocurrency such as Bitcoin in a digital wallet and due to the collapse of an exchange all the cryptocurrency you owned has disappeared, then it is likely you can claim a capital loss. This is likely to also apply if the cryptocurrency you own is stolen in a scam.
Unfortunately, it’s unlikely that a deduction can be claimed for people who have been scammed into handing over money for supposed “cryptocurrency investment” in schemes where no actual cryptocurrency ownership occurred. This is because they have not technically lost an asset, as they did not own the cryptocurrency in the first place, and the money invested is not considered a capital gains tax (CGT) asset under Australian tax law.