I went from three monitors and two computers to a 13” Chromebook laptop, because I traveled and worked remotely for six years. My focus and productivity improved, so did my customer satisfaction and income.
I still close every app not involved though. It's more efficient to reopen a browser window when needed than leave it in the background (and the back of your mind).
The solution that works best for me is just having a laptop. Instead of plugging in an external monitor my setup consists of using three virtual desktops:
1. Browser (lots of windows), chat clients
2. Code editor (lots of windows)
3. Terminals (one windows but lots of different terminals in split panes and tabs)
There are some scenarios where it would be convenient to have multiple things visible at once (browser + terminal to see log output for example), but the downside of becoming "dependent" on external monitors is simply not worth it for me. I'd much rather be able to work comfortably with the same setup anywhere (whether that's traveling or in a cafeteria).
The cheap monitor is for presentations - presenting stuff on a 4K usually leads to lag and doesn't look nice for people on their laptops. It works for things like documentation/Postman. The 4K is great for side by side code/comparing, or reading PRs.
A 4K monitor often works as well as two smaller monitors, especially if you work with something like Android Studio where code is on the left and resulting design is on the right.
Others feel free to chime in with their preferences too.