I am editing raw videos to upload polished ones to Youtube. I am capturing a game with OBS Studio, and the raw video output from OBS Studio is a sharp, high quality mp4. I then load that raw mp4 file into Movie Maker, and edit it by splitting, adding transitions, and a title slate with text. I export the video as an mp4 file using a custom setting (I've also tried using the "for high-definition display" setting as well), as a 1280x720 video with a 24000 kbps bit rate (and 29.97fps). However, the output video is not as crisp, and the colors are muted. I have tried using the maximum bit rate allowed in Movie Maker and this had almost no impact on the video quality or video size. That suggests to me that the problem may be with the importing of the mp4 file, but I can't figure out why it would be doing this. I have uploaded small portions of screen captures from before and after (pre-import and post-"high-quality"-export) to illustrate the quality loss I'm seeing.

Can anybody explain why this might be happening, and, especially, what can be done about it?