No. macOS shows one Dock, on one screen at a time, and there is no setting or third-party app that changes it.
What you can do is choose which screen it lives on, and move it to another one on demand. Both are below.
The Dock is a single process drawing a single window. It is not duplicated per display the way the menu bar is, and Apple has never offered an option to mirror it. No preference, no hidden defaults key, no utility. If a page promises you a Dock on every monitor, it is describing the menu bar, or it is wrong.
This is one of the few Mac Dock questions where there is genuinely no workaround, which is why it is worth saying plainly rather than burying it.
Most people who search for this are not really asking for two Docks. They are dealing with a Dock that keeps moving between screens on its own, and they want it available wherever they are working.
The Dock follows your pointer. Push the cursor to the bottom edge of any display and hold it there for a moment, and the Dock relocates to that screen. It is not random and it is not a fault, though it feels like both when it happens mid-task.
If that is the real problem, the fix is the opposite of what you searched for: pin it to one screen so it stops wandering. That is covered in how to keep the Mac Dock on one screen.
Since you cannot have it everywhere, the next best thing is summoning it where you need it. Push the pointer to the bottom edge of the display you want, and keep pushing past the point where the cursor appears to stop. The trigger sits slightly beyond the visible edge, which is why it often seems not to work.
If the Dock is on a side edge rather than the bottom, aim for that edge instead.
Open System Settings, then Displays, and click Arrange. Drag the white menu bar strip onto the display you want as your main one. The Dock treats that screen as home: it lives there by default and returns there after sleep or reconnecting a monitor.
This does not stop it moving. It decides where it starts and where it comes back to.
The menu bar can appear on every display, which is where a lot of the confusion comes from. In System Settings, Desktop & Dock, under Mission Control, turning on Displays have separate Spaces gives each screen its own menu bar and its own full-screen spaces.
It does not do the same for the Dock. One Dock, still, on whichever screen the pointer last summoned it to.
Want the Dock to stay put instead of following your pointer? Still Dock, which locks the Mac Dock to one screen, pins it to the display you choose, without turning off separate Spaces and without moving it to an edge you did not pick.
No. This comes up often enough that it is worth being direct: no third-party app does it, because the Dock is a single system-owned window rather than something apps can duplicate. Apps that manage the Dock, this one included, can choose which screen it sits on, not how many.
No. It gives each display its own menu bar and its own full-screen spaces. The Dock stays single and still follows your pointer.
Because you pushed the pointer to the bottom edge of that screen and held it there, usually while reaching for something. It is standard behavior on every Mac with more than one display. See how to keep the Dock on one screen.
Yes, and that is the question worth asking. macOS has no setting for it, but the built-in workarounds and their costs are laid out in the multi-monitor guide.
No. The number and kind of displays makes no difference. One Dock, on one screen, on every Mac.
Related: keep the Dock on one screen and what killall Dock does.