Thanks for all the sources, very appreciate this.

As for the “expiration date”, Valve made some changes a while ago. And there were misinformation, but also because Valve changed this and did not explain it well to the public. I think the 14 days limit was treated as a bug later, but can’t find the source. And I know for a fact that its not 14 days, as last year in summer I had no internet for longer than a month if I am not mistaken. And some games were still functional, after 30 days. That is the Steam DRM only, so if a game has its own DRM and other checks, then that is a separate issue.

At the very latest with Steam Deck they had to do all of these changes, because using it offline for longer period of time is a totally normal thing to do on a handheld. Sadly its not very clear documented and communicated by Valve as far as I know, at least to the public for non developers.

I already researched it last year and did not come to a definitive conclusion. I only know that there were changes in recent years, that’s why I cannot trust old sources. Actually someone has to do a ticket and ask Valve employee directly. Someday I do this if there is still no answer.