Where to find plastic corner pipe cover
You have a lot of options with this one, since it's just peeking from the corner and not running along the wall (if the elbow were the opposite direction). If I were covering this, I would use some decorative wood and build 4 sides of a box on the top, bottom, and 2 faces of this PVC. It ends up looking something like this: https://www.wikihow.com/images/thumb/2/27/Hide-Pipes-in-the-Kitchen-Step-14.jpg/aid5958328-v4-728px-Hide-Pipes-in-the-Kitchen-Step-14.jpg
You could attach such a box to the wall with glue, or a hinge if you periodically need access to it (e.g. to check for leaks).

If you want to be less formal (this looks like a basement, so maybe the industrial look is OK or desired, even) they make pretty sturdy plastic boxes with squared sides, you could cut two sides off of one of these to hide your PVC. My favorite look is the Project Box (https://www.google.com/search?q=project+box) and these come in many shapes, sizes and colors and most feature a screwplate lid so you could still have access to the PVC inside.