I will check out Tunic, once I’m done with one or two more games that I have currently installed, but on your hypothesis of games being made with internet knowledge in mind or them just generally being harder: Most games today are (or can be at least) much more complex in their systems than previous generations. Take X4 Foundations for example. It has a properly living economy. As far as I know, no ship and weapon just get spawned in without someone having mined and processed the ressources to do so. The game keeps track of thousands of ships over a volume of tens of thousands kilometers. And since you can mix and match every ship with a huge amount of equipment options, you can’t just point at a single thing and say “If I do this, I win.” But it also has some obscure systems, I can’t deny. For example that you can use EMP bombs to steal building blueprints, so you don’t have to buy them.
So while some games absolutely are made with the intent that only those who use the combined knowledge of the internet have a chance at experiencing every secret (looking at you, Five Nights At Freddy’s), most games are just harder due to the tech that makes it possible to do a certain thing in the first place.
On the other hand, I remember Morrowind being mentally difficult in some respects because there are no quest markers and very little other help aside from what you figure out on your own and what gets written in the in-game journal.