Distribute free sex robots and humanity would depopulate within two generations. Even better if the humans don’t know they are robots and believe they are an actually human who the humans think they are in a legitimate relationship with. Zero bloodshed takeover.

There's more than one movie about aliens who use global warming to wipe out humanity. AI data centers seem to be doing just that in more than one way. No need for an alien invader though, even a primitive species adapted for all the nooks and nuances of the environment is far more adept at it, it just needs to be diseased.

Consider reading the book "Roadkill", by Dennis E Taylor

There are also rumors, which may be untrue, of a Majestic 12 committee making deals with aliens in exchange for tech. It may be that advances in semi-conductor technology are the "trojan horse," with AI being a natural and probable consequence of that which was genuinely discovered after the chip advances or with AI first being developed by government and then leaked to the public later via papers and then commercially made public, with the end result making the earth uninhabitable for humans. We also don't know if aliens and UFOs are merely biological life/advanced travel or if they are some sort of technological/bio hybrid. It's also possible that these are crazy rumors made up by people who can't fathom science. I understand the statistical and computational logic of AI, so that doesn't seem that crazy to me, but sudden semi-conductor advances seem impossible to fathom; but I could just be ignorant. One flaw in an analysis like this is that even without UFOs, aliens, and computers, humans were doing a great job of exponentially obliterating the normal natural environment just based on pollution emissions from cars and other processes.

Who knows?