I "liked" your post even though despite broadly agreeing, I am not sure I agree in practice that as much telegraphing is needed as you seem to suggest. Or maybe, I just like what you call "combat puzzles." Though this topic is also linked to dislike for the idea that if a player can't use any particular ability (or use it as effectively) in any given encounter (even if it is their best or favorite ability) that it is somehow unfair or "a gotcha." Not that I am saying you are saying that - but to me figuring out what works and what doesn't in any given situation (whether it be ahead of time or during the encounter or some combination) is playing the game.
I get what you're saying. I do consider telegraphing as a regular part of my duty as DM in describing a scene to the players. Telegraphing can be super subtle or even super-obvious - doesn't mean the players will connect the dots right away on obvious hints, either. I just really don't feel the need to completely hide anything from the players. And that doesn't seem to prevent the players, via their PCs, from interacting with the world and exploring and experimenting and
playing the game.
I'm also of the belief that you shouldn't negate a PC's ability that has consistently worked without some kind of fair warning. Kaiju too big for Sentinel to work in your world? As DM, let the player, whose PC has mastered that Feat, know ahead of time - at our table, I prefer to do this through some kind of telegraph (e.g. when describing the monster, add one extra line of description: "This guy looks way too big to be pushed around with any ease"). Then, even if the player misses the clue, when Sentinel fails to have effect, the player can be like "Oh yeah - that's what you meant!"
A real game telegraphing example from our table: our party was facing off in a random encounter against a Yeti in the cold Greying Wildlands and it was described as thick furred and with some icicles hanging off it. As a player, I had my wizard cast Ray of Frost. Doh! Immune to Cold! Such obvious clues in retrospect but I just got caught up in the moment and made a quick decision to use my only attack cantrip. I didn't feel "gotcha'd", just reminded that I should pay more careful attention to the DM's descriptions.
Or, early in another campaign I was DMing, I had the trope-ish troll at a bridge collecting tolls. But this troll had reddish-orange skin and steam coming out of its ears when it spoke. Fire would heal this troll! Of course, the party just paid the toll and moved on so we never found out if they figured out the clues or not. A DM's best laid plans...
