My current display set-up has my Macbook to my right and my 27" BenQ Monitor in front of me. The bigger screen displays all my work-related applications, while I use the other one for smaller applications like calendar, calculator, and Spotify.
For as long as I can remember, all my notifications would appear on my Macbook's screen. I never minded that before, but after getting into trouble for missing out on several critical Slack messages, I needed to do something about it.
Setting up multiple displays on macOS is pretty straightforward. You simply navigate to System Preferences > Displays > Arrangement and drag the screens to your liking.
Now notice the white bar on top of the small screen icon. Believe it or not, that actually represents the Menu Bar. It handles a lot of things, including notifications!
I simply dragged it towards the screen icon on the left, and after a few flashes, my 27" display became my main monitor (displaying notifications), and my Macbook was acting as the extension monitor.
Be careful though, moving the menu bar icon will rearrange your desktop. So if you have your applications organized across different desktops, consider cleaning them up first.
Hope this was helpful. Happy Coding!