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?
By setting expectations.
You’re all adults, and you’re all here to have fun. If you go and read the adventures and walk through everything with no surprises or challenges, then as the DM, I’m not having fun, and won’t keep doing it. If you steal the limelight from other players with your “secret knowledge”, they’re not going to have fun.
So if you’re going to read it, great, but use the power wisely, so as to not undermine the spirit of the game.