I am trying to add a matrix to my ODT document, but everything I find is related to the old format of adding a matrix.

I got to Insert > Object > Formula.

I then select the Square Brackets (Scalable).

It then comes up with `left [ <?> right ] `

I can then add the first row, but I do not know how to add another row?

Libre Office 6.0.73 on Elementary OS