How can I make the square only show the corners?

Question

Design

just like here

Answer 1

1. you can just make such corners with lines (make 1 and copy it, then rotate and mirror as you need)
2. you can create a square with a stroke and cover the unnecessary parts of the stroke with the fill color of the square
3. - create the main square and 2 rectangles.
- using Merge Shape Components you cut out

Answer 2

You can play around with the dash stroke.

Answer 3

If you need it 1-2 times, then erase or “translucently” cut off the excess.