You can add a rectangle and then modify the border color. Let me briefly share the steps with you.

Computer: MacBook Air

System: macOS12

Software: WPS2019

1. First, we open the Word document and click on the top insert.

2. Then we click on the rectangle and select a box.

3. Then we click on the top outline.

4. Then we choose red.

5. Then click Fill and select no fill color.

6. Such a red border is added.