It is simply too difficult to edit this formula editor with wps. It is recommended to use a powerful mathtype formula editor. Download one from mathtype, which can be used during installation. Enter the matrix in minutes.

How to Input Arbitrary Dimension Matrix with MathType

Open MathType software and enter matrix symbols under matrix category.

Place the mouse on the matrix element, click the format button on the menu bar, select the "matrix" option in the drop-down menu, and select "Add a row on it".

According to your needs, you can add rows or columns above or below, left or right of elements at will.

The above tutorial is from mathtype official website, with pictures in the original text. Here is just a brief introduction.

I hope I can help you.