The technical details are all right (or seem right to me, anyway), but this is too opinionated for my liking. No, you do not need a 4K monitor for software development. Some people might like them, some won't. [edit/clarification: someone rightfully pointed out that nobody will actively dislike a 4K monitor. I was unclear here: I meant "some people won't need them" more than "dislike them"] This sounds like when Jeff…
And some grow to like them - I used to scoff... before I tried it for myself.
I think as well, it depends on your eyesight, and also your workflows and apps. I use Rider (and previously Visual Studio), and these have a lot of panes/windows - it's really nice to be able to have the code front and centre, with debug output, logs and a command prompt in another screen, for example. Another example would be to have zoom/webex in one screen, while I'm taking markdown notes in another.
A good while back, I moved to a dual monitor setup at home (1x 3k in landscape, 1x 1200p in portrait), and a triple monitor setup at the office (1x 1080p in landscape, 2x 1200p in portrait). I also use a Dell screen manager, so I can easily setup regions that windows can snap to - for example, the portrait displays are usually split in 2 horizontally.
The triple monitor setup is admittedly gratuitous, but I'm never going back from a dual setup - it's just so convenient to have everything I need always there, instead of constantly flipping back and forth through the many windows I invariably have open. It feels like I'm context switching much less.