Surprisingly I figured the piano puzzle out myself and then got stumped on the keypad code afterwards. Getting to the secret area only made it worse as I thought the code had to do with countable things in the rooms shown on the cameras on the laptop.
I haven't thought about putting the letters on the knife into the pad as I did previously with the wall-safe above the bed.

Now there are already many explanations for the piano puzzle but they all sound too complicated. Let me try to explain it easier for future players...

Example:
The paper from under the table says
L (15) L (7) L (20)
R (5) R (24) R (6)

5, 1, 6, 3, 4, 2

You play the top numbers in the bottom order, which would be
R (24) L (15) R (6) L (20) R (5) L (7)

L means you play the #th key from the LEFT
(the piano keys are numbered up to 52 from left to right, so it's easy to find the L's)
R means you play the #th key from the RIGHT
(you'll have to count backwards, 52=1, 51=2, 43=10, etc. R24 would be the 24th from the right, or the 29th from the left)

The slashes and order are different each playthrough, so if you want the 5min medal you'll have to learn how to read the paper sheet. Luckily you can take it with you and view it while playing the piano, so you don't have to learn the sheet by heart.

I hope this helps anyone struggling there in the future, good luck!

Gets a meh. Several puzzles are too cryptic and hard and to understand. Especially the piano puzzle.

Had to look up a guide to figure it out. When the player has to look up a walkthrough to figure out how a puzzle works in your game, then it's bad design for a puzzle and defeats the purpose of having it in your escape game.

What's the song name? Seriously, I've been wondering what it is all these years but was unable to find the answer myself.

You dont need piano knowledge to figure it out but yeah the page is confusing.

the bottom numbers correspond to the sequence of the top numbers (the Rs and Ls), do them in the order of the bottom numbers

it does not correspond to the slashes, you do the amount of slashes it says.

honestly i'm stuck on the piano, does the numbers on the bottom of the note corresponds to the dashes like 4 is R 20 ////, i need help understanding