$ cat program test integer ::a(2,2) real :: b(4,4) a=1 b=2.0 b = b + a end program test gfortran doesn't give a "shapes not conformable" error. There is a PR #19754 and fix for the similar problem when arrays are of the same type. In this particular case arrays are of different types.
*** This bug has been marked as a duplicate of 23209 ***