This is not exactly a correct description. Unicode does not specify the appearance of characters, only their meaning. It seems what’s changed is the reference p

This is not exactly a correct description. Unicode does not specify the appearance of characters, only their meaning. It seems what’s changed is the reference presentation of the character in the Unicode tables, not the character itself. Unicode goes to great lengths to preserve backwards compatibility so changing the meaning of a code point would violate that principle. Your OS or application providing Unicode 15.0.0 support will not change the appearance of U+A66E. The appearance is dependent on the font.