Audacity isn't terrible at all. Shorter on features than programs that cost $500, sure. But it's far more capable than the vast majority of YouTubers need. More correctly, most people are terrible even with Audacity.
Turning the gain down on the Yeti can be of some use but you need to understand why. The gain is what determines effectively the sensitivity of the mic. You need to speak quite a bit louder if you're going to turn the gain down, otherwise you'll end up normalizing the volume and just amplifying the background noise later anyways.
Frankly, looking at the picture it even looks noisy.
First of all, turn off everything you're not using. Any device that is on in that room will contribute to the noise.
Second, you could try an old recording trick.
Get a moving blanket. One of those really thick heavy blankets you put between furniture to keep it from getting scratched in transit. Usually you can get them from moving van companies and they generally have eyelets along the edges too. Then throw some hook screws into your ceiling behind your chair. Hang the moving blanket there when recording. It should dampen the echo coming from behind you. Of course also make sure the Yeti is set to Cardioid to reduce the bounceback from your monitor.
