Concept from this song: https://open.spotify.com/track/5IcUCggbkww7Ew7tbsPZvH?autoplay_ok=1
A colony of 50,000 intelligent dinosaurs, (20,000 in one mothership, 20,000 scattered across about a dozen other colony ships, and 10,000 in other assorted small ships, none of who's location is known) have arrived in the solar system. They are biologically similar to an assortment of different dinosaur species which are somehow biologically compatible. We're going to handwave away the problem of how this is even remotely with the single word "epigenetics." Anyway, they all have extremely high intelligence, with their average individual having the smarts of one of our top geniuses, like Einstein or Euler.
They consider humans "too dumb for slaves and too tough for hamburgers" and will, if left to their own devices, factory farm humans to turn them into chicken nugget like creations. They have advanced technology, but not drastically more advanced (cold fusion but no ftl or antimatter, cancer cures but not immortality). They are a species with very long lifespans but very low fertility. They have used their advanced technology to construct a cognitive influence device based around radio waves. It is only sufficient to work on people below the mental age of 13, but it will make them fanatically pro-dinosaur and willing to do anything at the slightest whim of a dinosaur, including killing themself or loved ones. Up to the mental age of 15 it will have some effect, but only that equivalent to talking to someone quite persuasive, more inclined to take pro-dinosaur stances in politics and such. (This is MENTAL age, not actual age, so an Ender Wiggin-esque figure would be not harmed, while, say Kayne West would be impacted) After the invasion was discovered, about 3 percent of the adult population converted to the Cult of the Dinosaur Mothership, a cult which worships the dinosaurs and will do anything it takes to see the succeed.
The reason the dinosaurs don't use RKVs or anything is that they want to farm the humans and need the earth to be habitable to colonize it and live there. Their home-world (well, their original homeworld was Earth but they were forced out of it, this is their main system) has been destroyed, they are the only members of their species remaining. One singular dinosaur, has defected and allied with the humans, giving them detailed knowledge of their plans, including the designs for factory farms. As such, every world leader, and the vast majority of the population is now completely radicalized against the dinosaurs, willing to do everything it takes to see them defeated (the plans for human factory farms also caused a massive outcry against animal factory farms, now illegal, and the considerable majority of the population is now vegan) including use of nuclear and other WMDs.
However, nothing supernatural has occurred to the human population, they are not "bloodlusted," but there's a massive degree of unity among the world population even greater than Britain or America in World War 2. Similarly, the Dinosaurs are not bloodlusted and can be persuaded, however this would be similar difficultly to convincing every human to become vegan (But hey as I said earlier that practically just happened so it's not impossible!), they are incredibly nationalistic and loyal to their species (That was why there was only one defector). Every ship and device of theirs has cloaking including near perfect thermal emission control and almost clear using advanced lenticular lens arrays. They can be detected but not easily or passively. For instance the Vera C. Rubin observatory would be able to see it in it's image but only with hours of data analysis. Once you know where they are, they're relatively easy to track though, assuming they don't go behind a moon or something (Basically this is to prevent "we just nuke them in the first 5 minutes no chance"). They start out about as far out as Uranus when first detected. They have decent but not perfect knowledge of humans and culture as around 5 advance scouts spent several decades surveying the planet in UFOs.
Feel free to ask any questions my worldbuilding probably has some holes but I did my best to make it airtight.