I’ve Been Killing Slimes for 300 Years and Maxed Out My Level, Vol. 9 (manga)

I’ve Been Killing Slimes for 300 Years and Maxed Out My Level, Vol. 9 (manga) by Kisetsu Morita. A Comedy manga rated Teen, published in English by Yen Press in 2021.

After working herself to death at an office job, Azusa is reborn as an immortal witch and decides to take life easy. Three centuries of casually defeating slimes later, she's somehow hit the maximum level, and news of the world's strongest witch brings a steady stream of challengers, dragons and new family members to her quiet countryside home.