I thought this was an interesting question about something I never had need to think about. Based on some replies, I suspect other users are the same.
Although I use a windows 10, 3840 x 2160 res 15 inch laptop which has been connected to a 1920 x 1080 res 23 inch TV screen as a monitor in a dual screen setup, there is not much difference in the text and APP size (Coverage) on either screen.
This is simply because the computer operating system is set by default to display content at a sensible size. I expect Apple do the same, by default. You can tweak this percentage to match your eyesight and preference.
For example, the small laptop screen magnifies the image by 175% (in my case) but does not alter the monitor image.
On that basis, you should have no practical issues with working on a high res monitor.
HOWEVER, what you will need to think about is the physical size of the screen and your distance from it.
https://www.bing.com/search?q=smallest+ ... A1&PC=DCTS
The above chart shows viewing distance in relation to screen size and resolution.
I expect you will buy a proper Pro monitor, not a 4K TV screen for work. Note that 4K TV screens start at 43 inches which is unsuitable as a monitor. You will destroy your neck, scanning from side to side.
I hope this helps.
