Dredging up a question from "Related" to provide more data.
Here we can see that the door panels themselves have no mechanisms of any kind:
Geordi is thrown through the pocket doors which reveal themselves as simple panels, either made of wood or plastic (maybe metal). All the mechanisms for operating the doors appear to be in the walls.
There's no equivalent shot of the doors from TOS, but various close up shots fail to show any sort of door hardware.
The locks were as the accepted answer said; the computer refusing to move the doors. If you wanted to pry them open, you had to use manual force.
Now, the doors to the Holodeck doors (and sometimes Cargo Bay doors) imply a locking mechanism:
But even those show no hardware, so maybe the extra bits are mostly designed to survive the type of impacts we saw in the first picture.
When Starfleeters need a door to absolutely, positively stay closed, they (1) lock the door with the computer, so it refuses open commands, (2) disable the manual release mechanism, so that the intruder can't just pump the door open, and (3) put up a security field or increase the structural integrity field on the door.
It seems to be a lot of extra effort to install SIF and security field emitters on all the doors, but it makes sense in the Trek universe; a physical, mechanical lock doesn't put up much resistance in a world of transporters and phasers that can vaporize just about anything. Physical doors are for privacy and basic protection against an unmotivated intruder (like a chain or bar lock; enough to avoid unintentional intrusions and signal privacy, but not enough to stop somebody truly motivated to enter.)