i want to ensure that RBF will not be used at all and nobody can change or cancel that transaction.
Then you will need to use some old wallets that do not actually have an RBF opt in. The two wallet I think of now is mycelium and trust wallet. But even though I don’t think someone without access to your keys will not be able to cancel or change your transaction with or without RBF feature.
is a miner or pool able to override the RBF DISABLED setting and still advertise my transaction with RBF flag enabled on mempool?
The issue now some mining nodes actually have Full RBF opt in and if the server is use to broadcast your transaction I think that makes the transaction an RBF enabled.