I have a two monitor set up. On one of them, I keep the same windows always opened for quick review (trading charts). On the main monitor, I often click on the "show desktop" button to quickly lower all the windows. Doing so also affect the other monitor...
Is there anyway to have the "show desktop" button only work for the main monitor?
Unfortunately, that is not possible on vanilla Windows 10. The "Show Desktop" button is there so you can easily clear you entire workspace quickly. I believe you can hide the taskbar on the second screen, but that will not change the functionality of the "Show Desktop" button on the main screen.
Something you can look into is creating multiple "Desktops". Although I forget what they are, there are keyboard shortcuts that allow you to switch from one to the other. You can have one "desktop" setup for whatever you are currently doing, and the other "desktop" setup for your trading charts.
