That's not a Steam thing though, but rather the specific software. Steam explicitly has an exit path for the user if Valve disappeared overnight that allows their downloaded games to continue working offline.

The difference being that we are discussing platforms, not the things that run on those platforms.

Steam Offline wants you to go online and perform a bunch of steps, including launching games and then enabling offline mode. Every game launch is is probably a download of at least few hundred megabytes of data. And then every game requires its own networks where your account linked to steam acc, etc. and Rockstar games iirc it you must be online when you launch the game. So the fact that Steam client has offline mode is irrelevant and misleading.

That has not been my experience. Any online game is going to be its own thing, dependent on the choices of the game company. Inherently, Steam does not require all the steps you're describing.

Sidenote, but my experience with the Rockstar launcher has been absolutely atrocious, to the point that I just avoid rockstar at this point even though I'd otherwise be interested because I've been burned so many times. That's a Rockstar issue, not a Steam issue.

Doesn't Steam still offer an offline mode that works with most games?

In my experience, the Steam offline mode only works if your computer is actually offline (without any network connection); if you're connected to the local network but the Internet connection from your router is down, it still tries to connect to the authentication servers while starting up.

Rockstar games require you to have an account at the launch iirc. And this us kind misleading, because while technically Steam has offline mode, but not necessarily the games you purchased on Steam. But having a unified UX is why I want to use the platform like steam to begin with.

It does offer an offline mode. It does NOT work with most games, because the publishers literally can't help themselves but add more layers of DRM on top of steam DRM and most of those these days require always online connections.

Were you still connected to your local network? Next time it happens, try completely disconnecting from your local network before starting Steam, it seems to use the presence of a local network connection to decide whether to enable offline mode or not.

Have never had this problem. There must have been something specific to your scenario, like the game wasn't downloaded, or it's a specific title?