Notepad is little more than a wrapper around Microsoft’s text box control (and I suppose some AI API these days). It’s not part of notepad, it’s part of Windows itself. A great feature for most users, in my opinion.

The corrective part is in Settings > Time & Language > Typing > Highlight/Autocorrect misspelled words. You can download an alternative to Notepad and hope that it doesn’t integrate with the spelling API, but any update to that software might bring back autocorrect.

You might want to leave the highlight feature on so you get instant feedback on what words you misspell.

As for learning a language, there is scientific evidence that information sticks better in your brain when writing down things on physical paper than when typing. If you’re learning a language through random exercise, you might want to consider going back to pens & paper.