Chadwick Boseman, in real life, had colon cancer, and died in 2020 from it. He was, therefore, not able to reprise his role as King T'Challa, so they had to have the character pass of an illness, though they never said what the illness was. My understanding is that they had to rewrite the script for BP2. Instead of focusing on T'Calla and his son, they rewrote it to show different ways to deal with the loss of a loved one.