The isreal(M) calling sequence determines if all elements of M are real.

$\mathrm{with}\left(\mathrm{MTM}\right)\:$

$M≔\mathrm{Matrix}\left(2\,3\,'\mathrm{fill}'=3.5\right)\:$

$\mathrm{isreal}\left(M\right)$

$\mathrm{true}$