This fix only applies to your browser and not the Steam-Client.

Open prefered browser, such as Firefox or Chrome.

Login and go to your Artwork Page.

In the top you should see "viewing" and select "Grid".

Open: https://userstyles.org/

and install the "Stylish" addon for your preferred browser.

Visit https://userstyles.org/styles/173525/fix-steam-artwork-page

and click "install style".

The Result should be visible immediately:

The pixels are now gone and you will see clickable boxes. :)

Hope it helped.. ^-^