Yes, the drive is NOT what enables Hyperspace travel.

The "Hyperspace Drives" your people are discovering and duplicating are merely the activators, the "keys", to the actual mechanism that is not available for scrutiny. Maybe it is in an alternate parallel dimension, maybe it is something programmed into the very fabric of space.

As a current real-world analogy:
A 10th-century tinkerer would be quite capable of building a perfectly working light switch, if they discovered a couple of installed and functional working models.

They would be able to duplicate the copper contacts exactly, the steel casing with a different but good enough substitute, the insulation with a lot of experimenting. They could even duplicate, with effort, the screws and fittings needed to mount the thing to those mysterious copper wires in the wall. Or discover that the mounting is optional, just a good idea for safety.

But would they be able to understand, or duplicate the LED light that is mounted in the ceiling, and controlled by that switch? Even with full access to the lights, too? And how about just why those copper wires in the wall seem capable of making small lightning and heat, even death, when touched?

Your hyperdrives are the switches, which can be duplicated. Not the LED light which shines, and definitely not the power station and distribution network that delivers the power.

The Ancients put the dangerous side of Hyperdrive technology out of your reach, but made practical access to it possible.

Yes, the drive is NOT what enables Hyperspace travel.

The "Hyperspace Drives" your people are discovering and duplicating are merely the activators, the "keys", to the actual mechanism that is not available for scrutiny. Maybe it is in an alternate parallel dimension, maybe it is something programmed into the very fabric of space.

As a current real-world analogy:
A 10th-century tinkerer would be quite capable of building a perfectly working light switch, if they discovered a couple of installed and functional working models.

They would be able to duplicate the copper contacts exactly, the steel casing with a different but good enough substitute, the insulation with a lot of experimenting. They could even duplicate, with effort, the screws and fittings needed to mount the thing to those mysterious copper wires in the wall. Or discover that the mounting is optional, just a good idea for safety.

But would they be able to understand, or duplicate the LED light that is mounted in the ceiling, and controlled by that switch? Even with full access to the lights, too? And how about just why those copper wires in the wall seem capable of making small lightning and heat, even death, when touched?

Your hyperdrives are the switches, which can be duplicated. Not the LED light which shines, and definitely not the power station and distribution network that delivers the power.

The Ancients put the dangerous side of Hyperdrive technology out of your reach, but made practical access to it possible.

I chose LED ceiling lighting for my example as there is no ways a medieval alchemist/engineer could figure them out or duplicate them. With enough incandescent lightbulbs, a large team of willing volunteers, and enough time, I think that having such things to play with might be able to jumpstart a smart and diligent researcher to Edison's lightbulb levels of understanding. But a low voltage, non-heat source of light is several knowledge quantums further down the queue. We want the hyperdrive's actual mechanism to be similarly several quantums of knowledge removed.