My Mac is very slow and lagged while connecting with ViewSonic screen

My Mac started to behave unusually when I connected it with the ViewSonic TD2420 monitor. For example, it would take too much time to open a folder. However, when I went to "About This Mac", then it lists the TD2420 display and allows me to make some changes.

My questions:

• What's the issue?
• Is this screen non-compatible with macOS?
• How do I maintain good performance while my Mac is connected to the monitor?

I'm running macOS Catalina.

Solution 1:

Here is a list of factors that may limit you from running the monitor at optimal performance:

Graphics card drivers 
Video cable adapters 
Docking stations 

These are discussed in more detail at this site and it gives some instructions to get optimal performance from your Viewsonic monitor connected to a mac.

Also this site claims your monitor is compatible with Macs but the touch function doesn't work. See the image below of the last page of the link.