There are a number of ways to achieve consensus, rawtxapp is right in general that many decentralized parties need to agree. For Taproot in particular, it uses

There are a number of ways to achieve consensus, rawtxapp is right in general that many decentralized parties need to agree. For Taproot in particular, it uses BIP 8 (see https://github.com/bitcoin/bips/blob/master/bip-0008.mediawiki https://github.com/bitcoin/bips/blob/master/bip-0008.mediawi... and https://github.com/bitcoin/bips/blob/master/bip-0343.mediawiki https://github.com/bitcoin/bips/blob/master/bip-0343.mediawi... and more generally https://bitcoinmagazine.com/technical/bip-8-bip-9-or-modern-soft-fork-activation-how-bitcoin-could-upgrade-next https://bitcoinmagazine.com/technical/bip-8-bip-9-or-modern-...) with LockinOnTimeout=true. The effect of this is that miners cannot block the upgrade so long as the (eventual) majority of nodes wishes to have the upgrade, they can only hurry things along and mostly protect the minority of older clients who have yet to upgrade.