I’ll strongly agree that this is the most difficult and time consuming step of reassembly. As Pau has stated it is vital that the cables are layered in the correct order before you begin attempting the connections.
Check back to Step 21. It’s not clear from the photos, but the ribbons can be run under each other. The display connection and the home button connection can become transposed at Step 21.
If in doubt, check the size of the connections and re-order accordingly.
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