Something I'd never seen before

[canetoad]

1. Answering my own question

The are called 'Fog bows' or ghost rainbows. Below is a good article describing the phenomenon with some stunning pix.

https://www.abc.net.au/news/rural/2023-03-23/fogbows-ghost-rainbows-weather-phenomena-seen-in-queensland/102123726
"They are fairly common in some parts of the world, but you wouldn't say they're common in Australia and the reason for that is the angle of the sun," said the ABC resident meteorologist, Tom Saunders.