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Hash power held by the pools supporting Taproot - Source: Coindesk.
In total, just the 5 pools BTC.com, Poolin, Slush Pool, F2Pool and AntPool represent 54% of the hash power of the BTC network, as shown in this graph.
So

how sure is BTC to be decentralised?
You're stupid beyond repair.

3 pools and here is >50% shitshowSV hashrate, that's your lucky day, usually 2 pools are enough.