Not sure if this is still the case, but with Steam it used to be that if you didn't put the client into "offline mode" ahead of time the client wouldn't open, let alone allow you to launch a game once the connection was lost.

I hope they took care of that by now.

[–] Nibodhika 1 points 7 hours ago

At least in 2013 when I started using Steam more seriously if your connection dropped it would prompt you asking if you wanted to switch to offline mode. And I know this because I had Steam on a laptop that I carried in my bag hibernating and I didn't had internet in some places I went to. So that has been fixed for over a decade.

[–] [email protected] 3 points 11 hours ago* (last edited 10 hours ago)

Pretty sure they did a while ago

Especially with the steam deck, you're not going to have Internet available everywhere