On my Surface Pro 6 I can not edit any notes using the on-screen keyboard.
Yet the on-screen keyboard works with new Notes.
I have had the same problem with my Surface Pro 4 for the last 4 years.
It seems Evernote are not bothering to support non - keyboard devices for its Windows App.
Goodbye Evernote, its been a good 7 years but now I am going to have to move on.