Your TV is playing a large part in the degraded visuals. It may be receiving a 720p signal from the Steam Deck, but it then needs to upscale that to whatever resolution your TV is displaying. Most TVs are hot garbage at doing this task, and will make your picture look washed out, or even pixelated.

The dock you’re using could also have subpar power delivery circuits. Even if this isn’t the case, make sure you’re supplying power to the dock via the Steam Deck’s charger (or one with equivalent power ratings).

These are problems I’ve never encountered in my ~2 years of owning a Deck myself, but I can’t give you more feedback without knowing what specific Dock and Television you’re using.