The Mac Mini 2018 comes with Intel UHD 630 graphics without a possibility to upgrade unless you use an external eGPU.
I was a bit worried about how it would perform with a 4K monitor scaled at 2560×1440. I use 27 inches 4K monitors and they need to be scaled to 2560×1440 as MacOS default resolution from a 4K monitor (3840×2160) is 1920×1080 and that is way too big for 27 inches.
The problem with scaled resolutions in MacOS is that they degrade performance, as internally the resolution needs to double and then be shrunk down. In my case 2560×1440 is in fact 5120×2880 (5K). As the warning mentions when you scale in System Preferences->Monitors “Using a scaled resolution may affect performance”.
I bought the base configuration Mac Mini in 2020, the 2018 Mac Mini in 2020 comes with 256GB SSD PCIe and the same Intel Quad-Core i3-8100 (graphics UHD 630) and 8GB of RAM.
My plan was to upgrade the RAM myself and save some money and I did to 16GB.
When I initially tried the Mac Mini with 8GB of RAM and scaled resolution there was some noticeable slowness (visual lag and stuttering) in the UI, most noticeable to me when scrolling and on entering/exiting Mission Control. I was getting a bit frustrated/worried but the strange thing is that the graphics history in Activity Monitor didn’t report large spikes in usage during those actions.
After upgrading to 16GB of RAM it felt much smoother. Probably not as smooth as running default scale but for me it has been working fine.