These are diffraction spikes [0], caused by the support structures that carry the secondary mirror. The shape of the spikes are influenced by the arrangement of the struts. Here's a better researched answer of the same: [1]

0: https://en.wikipedia.org/wiki/Diffraction_spike 1: https://www.quora.com/What-will-the-diffraction-spikes-on-st...

I am seeing multiple stackexchange answers that suggest this is due to an intentional over exposure: https://space.stackexchange.com/questions/58624/jwst-aligned...