Details: More information can be found at https://myanimelist.net/manga/109032/Yasei_no_Last_Boss_ga_Arawareta
I think this is the official site, it’s in Japanese though: https://www.comic-earthstar.jp/detail/wildlastboss/
A Wild Last Boss Appeared! is another cookie cutter isekai story. It doesn’t do anything new, but if you like the genre, you’ll likely enjoy this.
The story is about a video game player who gets transported into the video game he plays. He turns into his character, which is a female, so he gets gender bent. In this world, the character he inhabits was an overpowered villain, so now he’s coming to terms with that.
It’s not an original story. There’s a lot of fighting. A lot of anime tropes. The art is pretty good.
Overall, this manga was just okay. Feel free to skip it.