While the simplest way to get games for the Steam Deck will be direct from Steam, there's a few other stores out there that do give some amazing deals and Fanatical is one of the best. Note: we're not currently affiliated in any way.
Originally called Bundle Stars, Fanatical (like Humble Store) offers up Steam keys and they also do bundles too. Seems they've been keeping a close eye on the industry, and they've tweaked their store now to offer up proper Steam Deck categories.
Not only that, they also correctly list games as either Verified or Playable with an explanation on what they mean — so they've done a bit more than just stick games into a category. This is actually great, and I hope we eventually see more stores do the same.