Doubt regarding dual channel MOSFET datasheet
This NTJD440 is a dual N-channel MOSFET meaning 2 NMOSFETs in one package.

The listed ratings are for ONE MOSFET. It would be very confusing of the combined rating was listed. Also note how in the drawing there is no connection between the two devices:



that generally means you can treat them as if each is a separate device.

It is listed that the maximum \$I_D\$ is 0.63 A. Nowhere does it state that this is the combined current (it would/should state that as: \$I_D = I_{D1} + I_{D2}\$ or similar).

So the 0.63 A is per device.