5k display? You cannot use a toolbar in many programs with 4k. You cannot make bigger.
I use 1920 x 1080 screen resolution so I can easily see the buttons.
I suspect people who use 4k and now 5k create those hard to read websites with tiny fonts.
Another one from the Peanut Crowd (PC) ignorantly chimes in. I use a 27 nice 5K iMac at work. What you complain about is not a problem with a Mac. . . Unless you use a Windows virtual machine in it. Windows has problems with such high resolution screens and adapting windows and webpages to high-definition screens. Macs do not.