Perhaps he is trying to hide his true self. He may have a side of him that he doesn't want others to discover, like some special abilities or a different origin. So, being cold to everyone helps him keep his secrets and avoid getting too close to people who might figure him out.
One way could be through persistent kindness. If they keep showing him genuine care and kindness without expecting anything in return, over time, he might start to open up.
It could be that his new 'godlike' power has isolated him. People might be either in awe or afraid of him, and he may feel that he can't be close to others as before. So he acts coldly as a defense mechanism.
His closest friends like Ron and Hermione would probably be the most affected. They are used to having Harry around and relying on him. His sudden ignoring would leave them confused and worried.
One reason could be a misinformation campaign. Some malicious wizard or witch might have spread false rumors about Harry, making everyone believe that he has done something terrible like being in league with Voldemort again.
The abandoned concubines in different stories had different endings. In " The Abandoned Concubine of the Cold Palace," Yan Qingqing drank the poisoned wine given by Emperor Pei Yuanhao and walked out of the palace with the help of Empress Chang Qing before she died. In the story of " Reading a Book with Her Best Friend," Lin Xiuwan was dressed as the abandoned concubine of the Cold Palace. The story was not over and the ending was unknown. There was also Nan Sheng, who was dressed as the abandoned concubine of the Cold Palace. Her original body slipped out of the Cold Palace and fell into the water when she went to the lake to relax. The ending of the abandoned concubine of the Cold Palace in " Dressed as the abandoned concubine of the Cold Palace and was favored by the cold emperor alone " was not mentioned.
Harry would likely be devastated. He has always been in the spotlight, whether he liked it or not. Now, being ignored, he'd feel like he's in a different world. He might start to isolate himself even more, thinking that he's better off alone. However, he also has a strong sense of justice. So, he'd start to investigate. He'd look for any signs or clues as to why everyone is ignoring him. He might even suspect some dark magic at play. As he digs deeper, he could become more self - reliant and less trusting of those around him until he figures out the truth.
It could lead to a lot of conflict. His friends might try to reason with him, but if he's too angry, he might push them away. This could split their group apart, creating new alliances or just leaving Harry isolated for a while. His anger can also attract the attention of the wrong sort of people, like those who want to use his emotional state for their own gain.
It could be due to a spell. There are many dark spells in the wizarding world that might cause a person to feel cold. For example, some curses can drain the warmth from a body. If Harry was targeted by such a spell, he would be cold. Also, it might be related to his emotional state. If he was feeling lonely or scared, it could make him feel cold inside, just like when people are in a bad mood in real life, they might feel colder than usual.
In some fanfictions, Harry might use his knowledge of magic in unexpected ways. For example, he could combine spells in a new and creative manner that others haven't thought of. This gives him an edge over everyone.
Yes, it is quite disturbing. Harry is typically seen as a hero, and the idea of him killing everyone goes against his fundamental character. It subverts the positive and heroic image that fans have of him, and it involves a lot of death and destruction which is generally not pleasant to think about.