Anyone know how to get these blinking lines in my tool path window to stop? I can barely see the loaded gcode and the lines blink really fast.

We have seen this from bad OpenGL video drivers with intel chipsets. Roll back the driver if you can or upgrade. Could you please tell me what you have for a video card/chipset.

I have the Intel UHD Graphics 620 card. It is strange because I have Mach3 as well and it doesn't do it.

That's because we used the OLD OLD OLD way of doing OpenGL in Mach3 (and Mach3 is that old). In mach4 we are doing the modern Vertex Buffer Objects with custom shaders and so on. Mach3 used a genlist and is very primitive (openGL Version 1 stuff). SO.. when we startup we ask what version of OpenGL the card supports. intel lies and says it can do the modern way of showing the toolpath. So I don't know if this will work but under config toolpath set Mach4 to NOT use VBO's and lets see if that fixes it up.

hmmm.. that did not work, still have the flashing lines

Try the line OpenGL mode.. the sure fire way is to change the video driver.

Changing the video driver is not the solution. I run higher requirement graphic software on this all the time with no issues. The issue is in Mach4.

How do you switch it to open GL?

Okay, but I can 100% tell you it is the implementation of the OpenGL driver. I even got a PC just to test this! I was in hopes they would fix the driver but no such luck . The old version worked. I know what it looks like on the outside but please trust me I really do know the answer to this! I will see if I can find that industrial PC I got in for testing and try to get it to work again.

Here is what I have running for a test and please tell me what you have so we can see if we are even close.
Mine is working... this was the one that I got the report from an OEM of it not working on.
Intel HD Graphics 620
Driver Provider Intel Corperation
Driver Date 8/5/2020
Driver version 27.20.100.8587
Driver Signature Microsoft Windows Hardware Compatibility Publisher

I am going to see if I can update ... If all is what I think it is it should stop working and have the issue your seeing after update