Why Camtasia always produce video with a low quality, even if I record in 1280p, for example? I spent some time learning this tool, but I'm disappointed because I cannot produce video enough quality. Look for that, firt I have a screen snippet of the video still inside the Canvas on Camtasia, it have a nice quality, and below that I have the same snippet of the video yet produced by Camtasia, in MP4 format - low quality.

I'm not referring to the size of the screen, you can see the difference in the quality of the video, it have blurry and a bad color... If I'm not wrong, I've recorded and produced in 1280p or 720p at least.

Someone can help? Or at least, say to me that "it is just a problem with my PC and Camtasia are not that bad guy, Camtasia CAN PRODUCE IN HIGH QUALITY!". I spent most of my time learning it.
The quality of the images you posted look completely normal to me for what you are doing. You're taking a screenshot and scaling it down. That means that anything drawn as a single pixel in the user interface is going to become less than a pixel wide in the final video, making it seem soft.

You have a few options to deal with this. You can set your screen size to the final video size, or set it so the area you're recording is the final video size. Or you can leave the screen at full size and pan it around as the user moves the mouse. You'll still get some softness due to the compression, but it should be considerably less if you aren't scaling the video.