I used a typing website a while ago called typing club. In it, when you got a letter wrong, it would flash ontop of the letter you are on the letter you actually typed so you could reposition your hands to type it correctly. https://www.youtube.com/watch?v=0oxHTxhmcIo (video of what i mean, feel free to skip ahead until the guy gets a letter wrong). It would be nice if TU had this.
Speaking from an extension I like to use - TypeFU, I also think it should play a noise like an error, or buzzing when pressing the wrong key so you know “oh crap!”.
it does make a noise when you type a letter wrong theres just no indication of what letter you are typing that isnt the one you should be