During The Second World War about 70 million people were killed. Each of them deserves to be remembered.
The United Nations yearly commemorate the death of 5-6 million Jewish people. Instead, they may designate a special day to commemorate the killing of all 70 million people during the Second World War.
If particular populations should be mentioned for large numbers of casualties, we may consider the killing of about 27 Eastern European people, and 20 million Chinese people.
Better would be for the United Nations to designate a special day to commemorate all Second World War victims. If particular populations should be mentioned for the size of ethnocide, the Chinese and the Slavs may come first.
https://en.wikipedia.org/wiki/World_War_II_casualties
https://www.un.org/en/holocaustremembrance/2020/calendar2020.shtml