Very generally, what is your work? If some part of it is "monitoring", maybe some metrics or live orders of some kind then having it permanently on another monitor is a no brainer.
I generally do all my work on one screen and keep email / teams / Spotify on the laptop screen.
I work in the high end managed WordPress industry as Customer Success Manager. At any moment I have Slack, Tickets, Live Chat, Shell to several servers, and my server monitoring system up. ADHD means "out of sight out of mind" and so it's all visible all the time.
You know, it's funny. I believe I'm similar to you in this department. I use a giant 4K monitor as an ADHD mitigation tool.
But I used to work with another guy. Also ADHD. And he said he absolutely had to restrict himself to smaller, single screens, in order to focus because looking at multiple windows at once was anathema to his ADHD.
Just doubly reinforces how unique brains are. Even with the same diagnosis, different strategies.
I tightly control the amount of context switching I do since you can get derailed by them, for much the same reason. I don't think I have ADHD but I certainly struggle with attention, and that is a strategy I use. Every alt+tab/window switch is an opportunity for me to lose my train of thought.
Interesting, but this is avery specific condition (on top of every one is individual) vs a generalizing advice "you need at least two monitors" because for our work, it's true."
And not wanting to tell you it is wrong if this works great for you, but tbh I wouldn't see the necessity in this setup for multiple monitors, by your first post had assumed a very different kind of work ;)
I generally do all my work on one screen and keep email / teams / Spotify on the laptop screen.