This is a complicated topic with a lot of nuance. The TL;DR is:
Yasuke, the "black samurai" featured in the game was known to be a real life person
Whether or not he was actually a samurai is unclear, with rumours suggesting he was a samurai coming primarily from Thomas Lockley, who apparently falsified Wikipedia entries since 2015 to promote his 2019 book
One camp is calling people racist for having a problem with Yasuke's portrayal in Assassin's Creed whereas another camp is claiming people are trying to revise history and eradiate Japan's culture
The Japanese Government has launched an investigation about the game and Yasuke in general
Thomas Lockley has removed all social media presence