What Chris says. The likelihood that MATLAB can do something that PETSc or SLEPc can’t is very slim. But if you insist on reading large files in MATLAB (which itself is a rather bad idea), you could do the following.
load "PETSc-complex"
Mat<complex> dump(A);
ObjectView(dump, format = "binary", name = "A.dat");
In MATLAB, use share/petsc/matlab/PetscBinaryRead.m · main · PETSc / petsc · GitLab and do:
A = PetscBinaryRead('A.dat', 'complex', true);