The London Accords of 1953 & the Marshall Plan
Wow, I wasn't aware so many Global South countries forgave German debt after WWII. That context lends additional force to arguments for debt cancellation.
I happen to be working on a project about postwar Germany, so have a clarification to offer-- the Morgenthau plan was never really implemented, and US efforts on the ground were increasingly geared towards reviving German industry well before the Marshall Plan was announced. After President FDR suddenly died just before Germany's surrender, new President Truman provoked Morgenthau into resigning in July 1945 (link to Morgenthau's diary entries about what happened) https://fraser.stlouisfed.org/archival-collection/diaries-henry-morgenthau-jr-6880/volume-862-635446 Although the Potsdam Agreement set limits on the "level of industry" Germany would be permitted to pursue, officials US military government quickly worked to interpret the ceiling of German standards of living as a floor. The head of the Economics Division, General Draper, hired an external economist to write a report which concluded that the Potsdam limits were unrealistic (I have no opinion on what specific level was appropriate; but the vision of the economists within the US military government had a clear bent towards reviving German industry in a business as usual manner, with little attention to removing Nazi managers or other reforms).
It did take significant time to get German industry up and running; in large part because crucial coal mines were flooded. But there was never a comprehensive on the ground effort to implement the Morgenthau plan. I recommend the book Drawing the Line by Carolyn Woods Eisenberg to learn more about what happened. https://www.cambridge.org/core/books/drawing-the-line/46336A31FEA31DB0C768814B52C346EE