Im not reading LN, but from WN side it should be around ⅓ of the official main story (so should be around chapter 200-ish, but personally i would recommend WN as the after story is really expansive, one of the most expansive in the novel category with 1700+ chapter as of now and updated almost daily with no sign of author ending the series. The chapter includes well, exploring the trinia tradition, kaito networking event (like no kidding but it's a major spoiler), and more romantic and adding GF to his collection (either 10 or 11 iirc)