The Steam Deck is essentially a Linux gaming PC in handheld form, and it uses device drivers just like any other computer. That unfortunately means that sometimes driver issues can hamper the performance of the handheld gaming console. For example, the Wi-Fi connection may be slow, laggy, or could just plain refuse to connect. While you can still play most games offline, it’s not a perfect situation, especially if you were hoping to stream some games with GeForce Now or another cloud streaming service. You can always pick up a docking station if you need the most stability for your internet connection, but in that case you won’t be able to play it as a handheld, which is the biggest draw of the Steam Deck. As with any other Wi-Fi enabled device, there are a few things you can try in order to get your connection back online.
Source: xda-developers.com