A notepad isn't a bad idea, but they can do better.

The first improvement would be a spreadsheet, just a basic one that can do simple math. It wouldn't be hard to implement. Obviously, you can take notes in a spreadsheet if you want.

The next upgrade would be to offer an in-game web browser. This would let you take notes or run your spreadsheet using a web-based service as well as giving you access to web resources like Garlond Tools, Aryalla's, Lulu's, Icy Veins, Discord, Reddit, X, and so on.

Now I don't want any of these for myself: my spouse and I are PC players and always have at least a second monitor available. But given how heavily we rely on those second monitors, I can see people with only one monitor, such as console users, could use a way to do what I do on another monitor in the game instead.