During heart surgery, red blood cells are damaged. when the blood passes through the lymphatic system, these damaged red blood cells are trapped and broken down by macrophages. in which organ in the lymphatic system does the breakdown of damaged red blood cells take place?

The answer to this question would be spleen.

The spleen is an organ that has a role in immunity, breakdown of cells and part of the lymphatic system. In this question, the red blood cells are damaged and then broken down by macrophages. The process is similar to anemia hemolytic where the red blood cells are killed by the immune cells, except it was not caused by autoimmune disease.
In both cases, the red blood cell will be broken down in the spleen. If this happens for long time, the spleen to be enlarged to increase its capacity called splenomegaly.