[rmujica]

AFAIK in any network (including Bitcoin), any miner can select any transaction in the mempool.

There will always be a miner (or validator in PoS) that will be willing to take Tornado Cash fees.

[sph]

A miner can choose whatever fork they want, but if the other clients don't accept it it's effectively useless.

There is only one Bitcoin, and it's basically the chain the most clients are following. If you decide to follow another chain, you have created a new "coin", but Bitcoin is unaffected.