These screws are labeled as “M2x5”. I don’t think they’re 2.5mm, they appear to be the same as the 4 screws that hold the palmrest to the bottom shell in step 15.
Note that there are 4 flat “grabbers” that attach to flared posts on the back of the keyboard, so even when the 5 tabs are released, there will be some resistance, and you need to pull the keyboard straight away from the housing with a little force to release them.
I didn’t have a retaining clip on this connection, I was able to just gently pull on the black strap and it came directly away from the board.
I initially missed the step about removing the screw securing the black rail because I already had the Joy-Con “open”, to replace the joystick. IMHO the last slide should be separated into its own step — remove the screw, then slide the black rail out of the back housing.
Note the position of the little grounding rings when removing the red (10mm) screws. You'll have to make sure to re-seat them when reassembling!