Immutable X facilitates user to user trading, allowing you to buy individual cards from, and sell individual cards to, other users.
Card packs and chests are purchasable from the Gods Unchained shop which is separate to Immutable X. These transactions occur on the Ethereum network and still require gas. Once packs or chests are opened, valid cards will be minted to Immutable X.
Solving gas fees on pack purchases is a separate issue to gas fees generated by user to user trading. We are currently working on a solution, but at this stage purchases from the Gods Unchained shop will continue to occur on the Ethereum network and not on Immutable X for the foreseeable future. The current focus is to complete the projected Immutable X rollout on user to user trading.