Same source size; why does my final export looks so much grainier than the Premiere preview shows?

Hi all,

Another person asking about export settings here. I'm fairly new to Premiere but am getting more comfortable with it. I used Premiere to rotate the video by a certain degree plus change the aspect ratio for upload to Instagram.

I'm attaching my sequence settings, export settings, plus a screenshot that shows the vast difference in quality that I'm having trouble understanding. I looked at beginner Adobe tutorials and think I've followed the basic instructions correctly. I combed through some other posts asking similar questions and most people I saw were trying to get larger exports from small sources. But my source is bigger/the same size as my export and I just want the export to look as great as the preview shows it to look.

Thanks so much for your time.