Not to discourage further discussion, as there is always more to be said, but you may be interested in these previous questions: What were Nazi plans for their own soldiers who were disabled or mentally handicapped from war? and Were crippled Wehrmacht soldiers treated the same, or better than other handicapped people? (both answered by u/commiespaceinvader), and the discussion that takes place on this question: PTSD and the Nazi SS and Gestapo?

Although the linked discussions go into far more detail than I can, the TL:DR is that military veterans were broadly exempt from the Nazi euthanasia program. However, there are several cases where injured or disabled service members were euthanized (read “murdered”) by the Wehrmacht and the SS as the decision- making of the euthanasia program became less and less centralised, and gave way to the broader implementation of the Holocaust.

As you say in your question, those with PTSD were generally misunderstood, and the medical community (and broader society) of the time didn’t have the same conception of PTSD as we do today; PTSD wasn’t even a recognised condition in the 1940s. Therefore it is difficult to discuss how a society in the past treated or understood what is a very modern concept. However, the Wehrmacht did recognise the harsh mental toll that the war was having on their soldiers. These soldiers were labelled kriegsneurotiker (war neurotics), and sent to neurotikerlazarette (neurotic hospitals) for treatment.