there is no scientific evidence to suggest that aliens cause dimming stars. The phenomenon you might be referring to is likely the irregular dimming observed in a star known as Tabby's Star or KIC 8462852. This star gained attention because its light appeared to be periodically and dramatically dimming, which led to speculation about alien megastructures or advanced extraterrestrial civilizations.
However, it's important to note that the most likely explanation for the dimming of Tabby's Star is natural and astrophysical in nature, rather than being caused by aliens. Several hypotheses have been proposed, including the presence of a swarm of comets or fragments of a shattered planet in orbit around the star, or the effects of a dusty debris disk.
Scientists continue to study and analyze the data to better understand the nature of this star and its unusual behavior. But at present, there is no conclusive evidence to support the notion that aliens are responsible for the dimming of stars.