I heard that most of the miners are located in China. Thus we can say that most hash power is controlled by some regions. Can we still call Bitcoin decentralized if its backbone infrastructure is so centralized?
You heard it where? Please let us know the source so we can check if there is any truth in what you say because one search tells me that a lot are in America and not in China since mining was banned in China way back in 2021. But does this mean it is no longer decentralized? No. Of course not. The fact that bitcoin operation can't be halted just because one point was attacked makes it decentralized. There is no one point in which you can attack that would make bitcoin crash. So I do not know what you are talking about.