Is this a rainbow?🌈

No.

It's a defect of the lense system.

Rainbows don't intersect the Sun; they are light reflected from raindrops after being refracted inside them (splitting the rays into different colors). You have to be looking away from the Sun to see them.

Lens flare occurs when a point of light source such as the sun is much brighter than the rest of the scene, and it either happens to be in the image (within lens angle of view), or simply hits the front element of a lens without being present in the image. Depending on the position of this bright light source, it can result in a lot of haze/lack of contrast, orbs and polygon artifacts scattered throughout the image, semi-round shapes with rainbow colors, or a combination of all of the above. This happens due to internal reflections that take place inside the lens and even between the imaging sensor and the lens.

Read More: https://photographylife.com/what-is-ghosting-and-flare

Mmmnope

It's a lens flare