See the discussion: https://www.researchgate.net/post/What_is_the_reason_for_the_amorphous_halo_in_XRD_patterns_Does_it_have_a_relation_to_clusters_in_amorph_structure
Amorphous materials have diffraction patterns too! Just not Bragg diffraction from lattice planes. Here are some useful references:
Fischer, H. E., A. C. Barnes, and P. S. Salmon. "Neutron and x-ray diffraction studies of liquids and glasses." Reports on Progress in Physics 69.1 (2005): 233.
Egami, T., and S. J. L. Billinge. Underneath the Bragg peaks: structural analysis of complex materials. Pergamon, 2003.