Two monitors mirroring but only one appearing in 'Displays'
 

I have a MacBook Pro with M2 Chip and Targus DOCK423 USB-C Dual 4K and running two external monitors. Both monitors are mirroring each other but only one is appearing in system preferences in Displays. I have extended display selected and the laptop screen is extended from the monitors.

The product you are using does NOT have DisplayLink technology inside of it, so DisplayLink will be unable to assist you.

The product you are using appears to have a DisplayPort (note the 'Port' as opposed to 'Link') multi-stream transport (MST) hub inside of it. Mac systems do not support DisplayPort MST hubs, which is why only one display is recognized by your Mac and both monitors are mirrored.

Tagrus calls this out here --> https://us.targus.com/blogs/discover...plication-note

"Dual external extended rendering via DisplayPort Multi-Stream Transport (MST) is not available in MacBooks. When connected to a MacBook dual external monitors will mirror one another using Single-Stream Transport (SST). M1 based MacBooks will render to only one external monitor."