I don't have to worry about players reading my notes. English is my second language and short hand in Ukrainian is beyond a secret code.
I have no second language (so no excuse if I'm failing to communicate in English

I don't have to worry about players reading my notes. English is my second language and short hand in Ukrainian is beyond a secret code.
Puzzles inherently are completely metagame so that's a bad example. Player solve puzzles, characters can't.It doesn't matter why they cheat - D&D is a group game, and one person knowing all the answers, how to solve the puzzles, the secrets of encounters, or doing things such as your "completionist" argument where they must find everything, affects the rest of the group as well.
You can do that behavior all you want in solo games like CPRGs if that is what brings you pleasure, but selfishly ruining things for others for it is not acceptable.
Simply play stupid. With hold your DM knowledge. If you can't, then don't play. What is bad when you have DMs with photographic memories. I had one I thought he was cheating until his monk ran face first into lava......
When you play a game as a player you should refrain from reading material related to adventures. Source book are there for that. If you go into a game where you have read the adventure, you should warn your DM so that you can discuss how to avoid using "unfair" knowledge to your advantage. Such knowledge might come as divine insight if it comes up at all, but you should really tell your DM. It might even mean taking a back seat or simply retiring from that adventure....
But what if you are a DM that gets a chance to play for once? Chances are, you've read quite a bit of adventures, or at least parts of them.
The problem is that conversation rarely happens beforehand. Usually it comes up during gameplay when a player make a decision that is questionable of it being spontaneous decision or influence from past knowledge. The game grinds to a halt while the player justifies their action in the DM calls them names. Fun times.Well shoot If Clarence" completionist" has the bug so bad, just tell me. As soon as the module/ book is done, I will loan Clarence the module/book.
Down, boy. Down. No biting. Why is Barry "once bitten twice shy" biting me because their last dm sucked. Sorry that is an excuse. Thanks for playing. But Barry do that again and find another dm.
Puzzles inherently are completely metagame so that's a bad example. Player solve puzzles, characters can't.
You can dislike another style of play but calling it names and just dismissing it doesn't fix anything. All you're going to do is cause the player in question to selectively apply their knowledge.
if you don't like that style play that's fine but a lot easier to talk to the players and find out if you don't call them cheaters so they don't adopt a defensive posture.
It's like if I call you lazy because you don't want to take the time to make original content instead of running published stuff. You're probably going to get defensive right away.
Address the issue not the symptom.
I didn't attend for you to take the lazy example to heart. It was purely a framing Point of how useless name calling is. If offense was taken I apologize.I do not accept your reframing that cheating is merely a "style of play". If I had a d20 that only had 15+ on it, it would be cheating, not a "style of play".
So yes, actively cheating is a bad thing. Not just a difference in styles that one can like or dislike. Especially as it affects the other players at the table, something you have yet to address.
The funny thing is you try the sly ad hominen attack there to call me lazy - you are judging a style of play right there immediately after trying to defend cheating as just another style of play. (In fact, I haven't run a published module since the 1990s, but I play with DMs who do.)
If someone showed up in my game cheating like that, it would be his last time in my game. I don't tolerate cheating. Cheating is 100% always the fault of the player. Not the module. Not the DM. Not anyone else but the player.I believe it due to GMs having a higher tendency to be more active in discussing the game as a whole.
Most Published adventures are inherently flawed because anyone can pick it up and up and read it or if they run it again it loses it's replay value. It like the joke that idiots get twice a much value watching sports on TV because there may be different results in the instance replays.
It's also why I don't understand AL play.
Not really a good example of how player knowledge ruined the game but of how published campaigns should all have multiple angles of change to prevent static results.
Key takeaway: don't run published campaigns as printed.
You are also disregarding a player at the table by method of exclusion. Which is 100% avoided by not running published campaigns as printed. It takes less effort, more effective, and no one feels left out because they have seen it before.
Once or twice, since I DM and used to run a lot of modules during 1e and 2e, I played in a game with where a DM ran a module that I was familiar with. I always let that DM know and discussed the issue. Once the DM changed to a different module. Once the DM let me decide whether my PC would have figured something out or not, trusting me not to cheat. That put a lot of pressure on me as a player, since I had to really think hard about what I as a player would have been able to figure out, as well as what my PC would be able to figure out.However, if people pick up a module and read it, because they like reading this sort of thing, and it is before the campaign has been publicly announced, or before they join the group, how is that cheating? Just play as if you were the DM and had to run a character: Let the others make most of the decisions and only base your reactions off of what the characters know.