thanks for the info.
I’ve also used the M.NT68676.2 LCD driver board with the original power supply of the imac.
Initially I had also the BL_ON and P_DIM connected wrongly. Switching both of them fixed the issue.
I’ve re-used the cable that was going to the motherboard. For the moment just plugged in the cables in the connector and fixated using tape.
Still need to find a clean solution for attaching the control buttons of the driver board.