When I use a monitor with my Mac, it's to watch videos and multitask. I'd have a Chrome window open on my main screen in a virtual desktop and another Chrome window open on the monitor. When I switch to another virtual desktop on my main screen, then open a web link, OSX always opens it in the monitor instead of the other virtual desktop. I interacted with the virtual desktop Chrome window last. How can I choose to open links in the virtual desktop?
This isn't decided by the last interaction, it's decided by window enumeration.
By default, an external link will open in the first window opened in a browser. [Last would be more helpful, but that's not how it works.]
The only way to really persuade this to behave is to close all your windows, open one, then move it to the other screen. Then open a second on your main screen.
This behaviour may change after a reboot, when the windows open again. If you find a pattern to this, then it's just easiest to not fight it & move the windows to where you want them visually rather than by the contents of each.