How to disable these lines. and what are they indicating.
The screenshot isn’t very helpful to understand your problem.
Try posting a file.
You can upload a .3dm file by clicking on the vertical arrow icon above where you type a post, or by dragging the file into the are where you type a post.
That looks like something we see with buggy display drivers.
Open your V6 Notifications panel.
Is there a warning about old display drivers?