The 38" LG ultrawide has a resolution of 3840x1600 and it would land in the good (green) zone for non-retina displays with a PPI of approximately 110.
https://bjango.com/articles/macexternaldisplays/
I have a Dell U3821DW monitor with the same resolution connected to my Mac Mini M2 Pro, and it works really well. At the native resolution of 3840x1600 (PPI 110), both text and icons are clearly legible. It doesn't have the sharpness of a retina display because it's not a retina display. For my needs, the increased screen real estate more than makes up for the loss of retina sharpness. The only downside for me is that the built-in USB hub doesn't work with M2 Pro Mac Mini, although it works just fine with Intel-based Macs. So, I had to buy an inexpensive Anker USB hub to connect a bunch of USB devices (microphone, webcam, scanner, DVD drive) for which I didn't want to use USB C ports.
I didn't consider the 5K2K Dell U4021QW because the resolution of 5120x2160 at 40" diagonal would land it squarely in the bad zone with PPI of approximately 140. So, not acceptable at resolution native for the panel and likely requiring scaling to render an acceptable image. Of course, you could very well enjoy the tiny text and icons at the native resolution with no eye strain at all; however, there are too many reviews on YouTube suggesting that text and icons are positively tiny at native resolution.
You can read pros and cons at the article I hyperlinked above. There's also part 2:
https://bjango.com/articles/macexternaldisplays2/