I got a problem with the dark blue line, I thought this was a sharp sign, but after I pressed the Ctrl + E Clear Sharp button, but nothing happened, the dark blue line was still there.
I'm using Blender v2.81.16
With the default theme, "mark sharp" is a lighter blue. That dark blue is probably a Bevel Weight on the edges.
The easiest way to set them all to zero is to select the edges (or just all edges) in edit mode, and look under the "Item" tab in the right-hand sidebar (the one toggled with "N"). Look under Edge Data -> Mean Bevel Weight and set it to 0.
You can also use Ctrl-E -> Edge Bevel Weight, but that does a relative adjustment, so if you want to set it back to zero with the keyboard, you need to enter "-1 Enter" rather than "0 Enter".