@SotiCoto The menus and such are there so that the author can handle and show the readers progress exceedingly easily, plus they are often needed for the second most broken skill, universal appraisal. The same goes for levels. If it's game-turned-real, it kind of makes sense, but on the other hand, why are the NPCs suddenly real people? If the menus stay, then why don't the guards only ask you who stole your sweetroll, for all eternity? Because it would make the story deadly boring, most likely. These are just simply choices that reflect the author's ability and the market demands. A highly skillful author could as well write an idiotic story if they predict it will sell well and bring rice onto the table. Most isekai are trash and they repeat the exact same elements that are greedily devoured by the audience. That's how it goes. No need to try to reinvent the wheel, unfortunately.
As far as I can remember, the D&D rules books had the exp listed with every monster. Kill it, and you get that exp.