Received this MNDY2LLiMac 21.5-Inch "Core i5" 3.0 4K, Mid-2017 on 02/07/2020, it doesn't even run smoother than my mid 2015 MacBook Pro. I tried to upgrade the macOS Mojave that comes with this machine to macOS Catalina two times almost 3 hours both failed, the machine always show black screen during installation.I then created a bootable disk for macOS Mojave using my MacBook pro and tried to install it on the iMac at around 9:30PM, Feb 7, 2020, then I went to bed and let it run itself. The second day morning, Feb 8, 2020 I woke up at 6:24AM and went to check the machine, I found the fan was running at very high speed, and the machine was blowing out hot air from inside with a black screen. I tried to do a force shutdown and restarted the iMac and got a weird black and pink screen.There is definitely something wrong with this iMac. I had few MacBook pro in the past few years, and I've installed, reinstalled MacOS systems many times with no issues at all.This iMac is totally a waste of my time.