I noticed my cloud save wasn't syncing after exiting a game, and retrying didn't do the job. So I shut down and powered on again. The Steam Deck was stuck on the bootup logo for maybe 10 minutes, and then stuck on the Steam log-in screen for maybe 20 to 30 minutes.
My Internet wasn't down on my PC, and it looked like I was connecting on Wi-Fi just fine. At this point it seemed the problem was on Steam's end, but this page told the real fix, specifically:
Press the STEAM button, go to Settings → Internet, toggle Wi-Fi off, wait ten seconds, toggle it back on. If the network reconnects but still drops or runs slow, select the network, choose “Forget,” then re-enter the password. This clears a corrupted DHCP lease — the single most common cause of “connected but no internet” on Steam Deck, confirmed in dozens of SteamDeck subreddit threads.
