It's just dramatic light, not a composite. Last light of the day, filtered by a treelike on the left.

Yes that's where the treasure is buried

This was real, it's a single image and it lasted for minutes.

Here is internet link to similar:

https://www.bbc.com/news/uk-46434720

From their explanation: "Double rainbows, which follow the same arc as each other, occur when sunlight is internally reflected as it passes through the raindrops. Effectively another arc of light emerges but the resulting secondary bow is less bold in its colouring and the colours are reversed. You can see this in Gordon's Weather Watcher picture.
So what of the third bow? This is known as a reflection bow. Whilst rare, a reflection rainbow mainly occurs when the sun is lower on the horizon behind you (i.e. late afternoon/evening) and when you are near to a large body of water, such as a river, lake or sea inlet.
Sunlight reflects off the surface of the water and through raindrops, but at a different angle to the direct beam of sunlight."

There are rainbows, double rainbows and sometimes X pattern showing rainbows.

Link below describes...

This is known as a reflection bow. Whilst rare, a reflection rainbow mainly occurs when the sun is lower on the horizon behind you (i.e. late afternoon/evening) and when you are near to a large body of water, such as a river, lake or sea inlet.
Sunlight reflects off the surface of the water and through raindrops, but at a different angle to the direct beam of sunlight.