Had this problem earlier but no question answered it, and I figured out how to fix it anyways. I’m posting this in case someone else has the same problem.
The issue: The sun in the SunSky object flickers. The flickering goes away if TemporalAA isn’t used, but I would like to see if there is a way to fix the issue while keeping TemporalAA on.
The solution: Select the SunSky object and under the list of its components (In the “Details” tab), select the “DirectionalLight” component. Under the “Light” category, change the source angle to something above 1 (I have mine set to 1.25). This will make your sun appear larger (but not necessarily brighter). If you set it to 1, you might still notice a small amount of flickering, so the higher you set it, the less noticeable the flickering is.
What type of project is it in? ArchViz, 3rd person shooter, non-template based?