Not a QR code. Wonder if it's a graphics card glitch? Does it appear at the same location every time?

Not running any Chrome extensions that could be trying to add something ? Random websites or just the google page ?

Hardware fault or malware.

It pops up in random places, but at the moment it appears as almost like a bar code running across my desktop screen, which disappears when I open a browser. I am thinking this probably makes it a hardware graphics problem and not a malware or browser problem.

Might be just old graphics drivers. Try Windows Update to see if it downloads and installs a newer driver for you. The newer driver be hidden under the optional updates section. Look for Intel, AMD (or ATI), NVIDIA. If you see multiples, try and and see if there is one specially for graphics.

A search seems to find some good tutorials on upgrading you graphics driver (some using a different method to above) which may help you if you don't know how.

Run the classic benchmark  https://benchmark.unigine.com/heaven

IF that sets it off, you might need to clean your gpu fan and apply some thermal paste