In reply to Rxn;
I too (a fellow World of Warcraft Classic player) faced this issue recently.
I also have an MSI Laptop, and am also using the Dell D6000 docking station, connecting it to my screens using DisplayPorts.
However, I found the solution!
When I play the game on my laptop, I get about 100 fps.
When I connect it to the D6000 using USB C, fps drops to 12.
After inspecting my computer's performance in the task manager, I noticed that whenever the device is connected to the D6000, the usage of the NVIDIA graphics card drops to 0% and the onboard Intel graphics cards rises to 100%. When I unplug the usb C, the situation turns around.
This made me realise that I'm running the game on the wrong graphics card when the docking station is connected.
I tried various ways to resolve this issue (like setting the default graphics card for the game in the NVIDIA control panel), but none of that worked.
Eventually, I just disabled the Intel UHD graphics display adapter in my device settings.
Once I did that, FPS rises back to 60 fps (which is the cap for the D6000)!!
Please note that when you do this, it might have a significant effect on the battery life of your laptop.
Even though this is a year old topic, I hope this information is useful to some of you!