I heard that most of the miners are located in China. Thus we can say that most hash power is controlled by some regions
Like has been stated China was the highest before the 2021 ban because of their relatively low cost in power.
Can we still call Bitcoin decentralized if its backbone infrastructure is so centralized?
Yes. Bitcoin is decentralized in its design and governance
One can say mining is centralized, ownership centralised (large quantities own by institutions or exchanges)
Doesn't mean Bitcoin itself is centralized.