The curves of the letters are not smooth.
Converted to curves:
When exporting to jpeg, tiff, etc., this problem is quite unpleasant.
Both the images in your post look almost identical, possible due to saving them in a very low resolution and further degraded as this forum resizes the images to fit. Please post a higher quality of image or upload to a free online file storage and provide us links to them. It would help us help you better.
The image is not resized. Both at 300dpi and 600dpi is the same. For screenshots is increased 350%. Font is PF Agora Serif Pro Medium.