Here’s the simple answer: Immutable X covers the gas for you! Behind the scenes, Immutable X batches up transactions and is able to pay a cheaper rate to Ethereum for a bulk of transactions. Immutable X batches thousands of transactions for execution off the main Ethereum chain, and publishes a rolled up, zero-knowledge, validity proof of the transactions to the blockchain.
A single hashed proof validates every single transaction in the batch! More detail on zero-knowledge proofs can be found here, but what you need to know is that the massive reduction in data being written to the blockchain allows Immutable X to cover the gas for the entire protocol and to offer gas-free transactions to users
However, transactions that interact directly with L1 Ethereum cost gas because they can’t be rolled up in Immutable X. This means that depositing NFTs or cryptocurrency into Immutable from Ethereum, or withdrawing NFTs to L1 will cost gas.