Hi Doug,
If your monitor is 4K (screen resolution 3840 x 2160), try creating the final MP4 video in PTE AV Studio with the same pixel resolution of 3840 x 2160.
Check the quality of the created MP4 video in PTE AV Studio on your computer using VLC or Media Player. So, you can compare the visual quality of the original video and the published copy on YouTube. And determine where the problem occurs.
If the local video file quality is excellent (a picture is sharp), but YouTube shows poor image quality, check the quality switch in the bottom YouTube toolbar. Sometimes it automatically selects a low resolution (720 or even 480). Switch manually to 1080 or even 2160 if you created a 4K video).