Is it even possible to do this in 2025? Thinking about running some old published adventure modules, but I have a couple of players whom I suspect will run to the internet and peek at things only the GM should know. Other than re-writing the adventure myself, can I even guard against this?
You don’t. You just remind them that everyone is there to have fun. Since part of having fun is staying in character and taking on the adventure, if the player starts making choices that are obvious meta gaming like that, they just aren’t part of the group any more. Or, if it’s everyone, they can find another DM.
That may seem harsh, but it is possible to not only play while having read a module, you can even replay the exact same module multiple times. It just takes the players and DM being willing to do the work to compartmentalize the previous knowledge. That isn’t always easy, and not everyone can do it (much less do it well), but everyone can help each other to stay on track without “cheating”. I don’t consider prior knowledge cheating tbh, but a lot of people do
I agree. People generally are mature enough to keep meta knowledge from tainting their characters actions. To clarify: I don’t mean meta knowledge like HP totals if enemies or similar. Not using that kind of information would be against the spirit of the game (IMHO). But having a character act on information that is explicitly not available to that character (but may be to others).