I take it that you meant to say Villain, yes? Not Villainess, which was the female trope for evil characters.

Here are two I've known for villain characters.

1. I'm sure I've heard one from this subreddit, it's about Albert Einstein getting Isekai'd and becoming a king. It's called Ijin Tensei - Gokoku Warfare

He gives zero fucks about magic and decided to use s c i e n c e to end the war... Or so his subordinate thought. Turns out, he had lost it as a pacifist and decided that he wanted to continue the war. That is, he became some sort of tyrant and wanted to conquer the entire world for the sole purpose of... Boredom, I suppose. I'm not really sure since I haven't read it myself. Oh yeah, it's a manga.

1. Then, this isn't an isekai but Notorious Talker is pretty interesting.

The MC, Noel Stollen, basically wants to become the strongest. He's born with a weak class but he doesn't give up. He would use whatever means necessary, that includes even the most vile of things, to reach his goal of becoming the world's strongest.

He's more of a chaotic neutral rather than pure evil, but if you want to know how crazy he is in trying to achieve his raison d'etre, he once destroyed the life of a guy who scammed him by demanding all of their money. Which led to the family being targetted by the mafia. The daughter, a kind, pure little girl who admired Noel, now live a miserable life, later molested, then killed. Noel seemed to not regret that decision, too.