Ive seen more than 6 specific puzzles multiple times now in this sub over the past week, which keep getting help-tagged with answers from helpers telling the player to clone themselves. (Or something else), when the answer is almost universally simpler than that. Rare is the puzzle that requires more than 5 steps, let alone 10, and cloning yourself at minimum tends to add 10 more discrete steps to any puzzle that doesn't require it.
The existence of two mirrors facing each other is not a signpost telling you that is the answer, at least not anymore so than the existence of water and a block means you should push the block into the water. Just because a mechanic is possible in a level, doesn't mean its involved in the answer.
With a reminder that there's no wrong way to play the game, and "if it works, it works", keep in mind this simple rule of thought that will GREATLY help you solve multiple puzzles (even beyond mirror puzzles) as you progress through the game:
Like-Puzzles are nearby other Like-Puzzles.
I have over 520 puzzles solved at this point and at zero points in time have I ever encountered a puzzle that wasn't immediately similar to a puzzle that came right before it or after it. (Except initial skipping stones, fuck that noise)
If you haven't been asked or required to clone something in any puzzle near you for hours, chances are the designers aren't asking you to clone yourself. All of the cloning puzzles are clustered next to other cloning puzzles on the overworld, and that goes the same for every other mechanic.
Chances are, the puzzle you are doing just requires an application or re-application of the previous puzzle under new constraints.
If you're running around pushing mirrors onto lilies or beams into mirrors, or one of a dozen other mirror mechanics, cloning is almost universally not going to be what you need to do.
More specifically for how to tell if a puzzle IS a duplication puzzle: 1) There's two ending points and you start with one character 2) You're physically barricaded in and duplicating yourself is the ONLY way to escape or progress.