not when you're out and about. Steam Deck doesn't exactly have 4g/5g connectivity either....
exactly, I like to play a bit on my Deck over my lunch break at work (I made good progress in the Trails in the Sky trilogy the past few months thanks to that) but there’s no public wifi available where I work (and we’re not allowed to connect to the office wifi with personal devices)
I travelled around for most of August with my steam deck offline and didn't have any issues.
You just need to make sure your updates are complete and then set it to offline mode before you lose internet connection and you're good to go.
I will say, the one downside to offline mode that I’ve found is it doesn’t seem to track your playtime, so unless I know I’m going to be offline for a while I typically just leave mine in regular mode and let it be grumpy there’s no network to connect to (as long as I’m not playing a game with an online connection check this doesn’t seem to cause any problems)
edit: should note offline mode doesn’t track your playtime for things like stats but it does for things like refund requests, which shows they are actually tracking it but for some reason choosing not to show it for some inexplicable reason
honestly to me that’s one of the most baffling design decisions Steam seems to have made