They can't be display: none as that would mean the screen reader can't access them. To do this properly and help low vision people, you need to make sure the textarea is synced with the cursor position and that all the text is positioned roughly where the text on screen is. By doing this the screen reader will correctly outline the element being read.

There may also be additional costs like the string manipulation required to build the row text in the terminal, this is nothing that can't be optimized but then that's more memory and cache invalidation to worry about.