Fibonacci-style matrix expansion
MATL, 13 14 15 16 20 21 bytes

2*:"!tP2:Y)sv


Thanks @Zgarb for removing 1 byte!

Try it online!

2*         % implicitly input number N and multiply by 2
:          % create vector [1,2,...,2*N]
"          % for loop: do this 2*N times
  !        %   transpose. Implicitly input matrix in the first iteration
  tP       %   duplicate and flip vertically
  2:       %   vector [1,2]
  Y)       %   pick submatrix formed by the first two rows
  s        %   sum of each column
  v        %   append as a new row
           % end for
           % implicit display