INSANE, unusable lag when brushing in Lightroom

I have always liked the analogous description of 'Brushing' in this article by Victoria Bampton-

In-  Non-Destructive Editing

https://www.lightroomqueen.com/lightroom-performance-complete-series-optimizing-lightrooms-speed/

By the way, probably should have asked this first.

In LR click on Help, click on System Information, click on Copy. Paste that in your reply, from the first line down to just before just after plug-ins

Performing lots of brushing on a photo is known to cause this type of lag. 4K monitors make it worse. I note that you did not mention your exact CPU in your computer specs.

Some suggestions:

• Make sure GPU acceleration is off (you said you already tried that)
• Perform the brushing as the next to last step; and as the last step turn on transforms and lens corrections
• Use Photoshop to do the brushing

My hardware is not "state of the art", but working as an IT Tech the hardware should (in theory) have no problems doing the simple graphics editing I am doing."

Sorry, brushing with a 4K monitor puts a huge amount of stress on your CPU, and obviously you do not have powerful enough hardware to do this and expect reasonable response time.

Now what follows probably will not solve your adjustment brush lag issue, I think it is probably all those pixels in 4K.

But in the list of things you went thru to improve performance on a WIN OS rig, perhaps some tweeking is called fir..

‘’First up is Power Management, mind you fir a laptop, this one is not fir when you are running on battery. But the issue is to get the OS off a balanced setting to a High Performance setting:

Should You Use the Balanced, Power Saver, or High Performance Power Plan on Windows?

Then their us us lots of stuff running that can slow everything down:

https://www.cnet.com/how-to/10-things-to-disable-in-windows-10/

By the way, noticed NVIDIA, now this particular link is for another NVIDIA GPU, but talks of performance improvement tweak for their products in general.

How do I customize Optimus profiles and settings? | NVIDIA

and same from another source

https://www.winhelp.info/boost-lightroom-performance-on-systems-with-nvidia-graphics-chip.html

I see 4K display.

But what resolution are you running at? If at 4K, lightroom will slow down when filling in all those pixels, Reducing to a nit full screen might help a bit, but reducing down to 3K, or less probably will speed things up more.    

Be happy you are not on a MAC OS and cannot actually reduce resolution (scaling does not cut it)

Yes, you are not going to be happy having a nice 4K monitor and I Assume 4K capable GPU and not being able to leverage that, and you are not going to be happy that PS probably works just fine, just LR bogs down. but....