For the longest time I was frustrated with the lack of any sort of skyboxes for plain, ordinary nighttime stars. Usually, the ones you can find under “star skybox” or on the unity store are steaming hot trash.
Turns out, NASA and other people who own fancy telescopes seem to publish a lot of cylindrically projected maps of the stars, and as luck would have it, they work perfectly as skyboxes.
Straight off the internet!
Whoever wrote the image projection import settings for the unity editor is the real MVP here.
I uploaded a simple, non-virus unitypackage here. You can use whatever image you like, the good ones can be found on google, keywords “star sphere map”.