Are there any tools out there that allow you to mirror the dock on two monitors?
ActiveDock is a dock replacement that can appear on on all monitors - there’s also switch glass which not a dock replacement but does appear on all the screens.
Not that I know of.
At least, not directly.
Keyboard Maestro has an ‘applications palette’ which will show your running apps. So, in that sense it could be said to be ‘mirroring’ the dock by having another strip of clickable app icons.
There’s also uBar which is similar-but-different. It’s also not free, but is part of Setapp, I think.
I think SwitchGlass is as close as you may get. http://hypercritical.co/switchglass/
I’ve spent quite a bit of time with uBar. I really like the app overall and it does allow for a flexible dock-like configuration. Unfortunately it also has some annoying bugs. Most notably, Catalyst apps remained in the docked even after they were quit. I tried contacting the developer multiple times and didn’t receive anything but an automated response. I eventually gave up on uBar and went back to the built-in Dock.
Does it work in macOS Big Sur?
That’d be a question for Siracusa. My Big Sur machine is back on Catalina for the time being.