in my system (i don't know if in others it works in a different way), when a material is assigned to a region, nothing happens.

it would be useful to see, in the "command line" history panel or, if you prefer, in the model (for example, applying a color to region or to its edges) that the material was effectively assigned.

here the procedure:

1- add new material
2- select material in the list by simply selecting it by mouse
3 - press "Apply All" button to apply it to assign it to all elements.
when you do this color of the mesh will change and also you will see the type and name of material in the legend windows (left side of program).

this should do the job if not let me know.

BTW, for almost every command in ADONIS "Apply" is needed except drawings and some other navigation tools.

yes, just verified.
but if i first try to apply material to a region still not triangulated nothing happens.
this means that the order of action can not be changed.
well, i've learned another bit of knowledge of your software.

good,
and correct everything should be in order. which is from my experience in simulation is good.