Given the fact that I am working from home more and more, I have changed my desktop setup. I decided to sell my 2017 iMac 27 inch and to use a Mac Mini instead and to go for a big 32 inch 4K display also because of the fact that I do need to connect my work PC laptop due to its security infrastructure to the display.
Last week, I purchased the LG 32’’ 32UN880-B UltraFine. It is a fantastic display that works just great with both the Mac Mini and my work laptop.
I stumbled upon this display because it received an extremely positive review by prad.de, which is a very thorough and competent German display review website.
https://www.prad.de/testberichte/test-lg-32un880-b-perfekte-bildqualitaet-zum-genialen-preis/
(German, but I think your iOS 14 or BigSur Safari might be able to translate it decently, it is definitely worth reading.)
So, the question of this topic was iMac screen vs. 3rd party 4K displays… Is the LG UltraFine 4K as good as the iMac? Well, I do not miss a thing. The pixel density on the iMac is higher, but it is absolutely fine on the LG display. The iMac’s glass surface creates an impression of a tad more vibrancy, but the glass comes with the typical glare. The LG does not suffer from glare and the colors still look great. And 32 inches… Boy… I will not be able to go back to anything smaller…
Hopefully, Apple will have a 32’’ option for an Apple Silicon iMac in the future. 
What really pushed me over the edge is the price of the LG display. As suggested in 2019 in this topic, the prices begin to drop into interesting price ranges.