How does one remove this desktop that keep showing on right side when i full screen my videos online

I like to keep my system clean due to my ''OCD'' tendencies so i would appreciate your help.

I have no idea what you mean.

If you click on the uploaded image, there is an 'artefact' (strip) down the right side of the image. There was a similar thread on here recently about overlapping workspaces in a screenshot. @DaddyWmaker do you have more than one workspace? Remove any additional workspaces before using screencapture, just a guess.