Creating a Crossed Square

VBA Excel, 168 bytes

Instruction:

I find Excel with the help of VBA is an effective and a sufficient tool for this challenge. Set the worksheet of Excel like following

Yes, we use the small, classic square-shaped pixels like the old times by using the cells in a worksheet as the pixels. Ha-ha...

Here I use cell A1 as the input and I change its font color to red. Why red? Because red is three-letter-color so it fits for golfing. Write and run the following code in the Immediate Window:

N=[A1]:Range("A1",Cells(N,N)).Interior.Color=vbRed:Range("B2",Cells(N-1,N-1)).Clear:For i=1To N:Cells(i,i).Interior.Color=vbRed:Cells(i,N+1-i).Interior.Color=vbRed:Next

Ungolfed the code:

Sub A()
    N = [A1]
    Range("A1", Cells(N, N)).Interior.Color = vbRed
    Range("B2", Cells(N - 1, N - 1)).Clear
    
    For i = 1 To N
        Cells(i, i).Interior.Color = vbRed
        Cells(i, N + 1 - i).Interior.Color = vbRed
    Next
End Sub

Step-by-step Explanation:

N = [A1]: Range("A1", Cells(N, N)).Interior.Color = vbRed

Range("B2", Cells(N - 1, N - 1)).Clear

Looping through the diagonal of range cells: Cells(i, i).Interior.Color = vbRed

Final step and output: Cells(i, N + 1 - i).Interior.Color = vbRed

MATL, 20 19 17 bytes

2-:XdtP!+~TTYa1YG

You can try it experimentally in MATL online. You may need to refresh the page if it doesn't work.

Sample run:

ASCII version: 19 bytes

2-:XdtP!+~TTYa~42*c

Try it online!

JavaScript (ES6), 96 bytes

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