Latex generates pdf with black end of line

i just wanted to add that this black box is only created if you have the

\documentclass[11pt,a4paper,draft]{report}
                            ^^^^^

option set. It will leave if you delete this - and just appear as a warning in texfile.log such as

Overfull \hbox (38.36009pt too wide) in paragraph at lines 16--30
Overfull \hbox (6.07912pt too wide) in paragraph at lines 37--38

if i remember correctly.

Black rectangle is a sign of overfull. You have to increase a tolerance for example. https://www.overleaf.com/learn/latex/%5Coverfullrule

If it doesn't solve your problem you can get better help here: http://tex.stackexchange.com