The main factors to consider are differences in specifications between the editing screen and the viewing screen, as well as the impact of resolution when compositing (burning) text onto images.
Please check whether any of the following methods improve the issue.
Place "large text" on a "high-resolution image"
Prepare as large and high-resolution an image as possible (※), and place the text (Marking) at a larger size.
※Recommended image size: 1280px or more in width
Take a screenshot on the editing screen and re-register the image
For images that have already been registered, please follow the steps below to "enlarge and re-register the image."
- Open the editing screen and make sure the image is displayed in a large size
- Take a screenshot of the enlarged image using your PC's screenshot function
- Register the image taken in step 2 into the Step again
Related
Add markings and edits to images, such as arrows.
https://teachme.jp/8/manuals/4929404