I had no idea what this was talking about, and it appears to be because they've defaulted it to off for existing logged-in users. Maybe that's a way of reducing pushback.
In case you want to turn it on (or off), it's under Preferences->Appearance->Page previews. I think I'll probably leave it off personally. I like the previews that have already existed for a while in the mobile app, but on desktop not so sure.
That's what I meant, the previews are on by default for not-logged-in users, but appear to be off by default for logged-in users (or at least the preference was set to 'off' for me).
Perhaps you had enabled the beta feature and when the feature went to production the setting was kept enabled? Check under Preferences>Appearance>"Reading preferences".
Hmm, that could be it, since it's showing up as enabled for me. I have "Automatically enable all new beta features" on, so I guess I was just betaing this feature for a long time.
In case you want to turn it on (or off), it's under Preferences->Appearance->Page previews. I think I'll probably leave it off personally. I like the previews that have already existed for a while in the mobile app, but on desktop not so sure.