trying to display unusual matrix reboots calculator

[DrD]

Your OP contains the corrupted matrix:
[[1 2 3],[4 5 6],[7 8 9]]

If, instead, you use:
[[1,2,3],[4,5,6],[7,8,9]]

You will see that your example has a syntax error, (mine works fine on my devices). Copy these and paste them into your command line to easily verify this for yourself ...

You can also use: m:=[[1,2,3],[4,5,6],[7,8,9]];