I just bought a portable monitor to travel with, and setting it up reminded me how many useful Mac laptop features people never find. Here are a few I'd show anyone with a MacBook.
Use the right cable for an external display. You need a video-capable USB-C, USB4 or Thunderbolt cable. A plain charging cable often gives you a black screen and makes you think the monitor is broken. If the monitor came with a USB-C cable, start with that one.
Know your display limit before you buy. Some Mac laptops drive only one external display, some only from a particular port, and some only reach their maximum with the lid closed. A hub doesn't raise the limit. Your model's tech specs page on apple.com says which.
Plug straight into the Mac instead of through a hub. On an Apple silicon laptop, click Allow if you see the "Allow accessory to connect" prompt. Then open System Settings › Displays, hold Option, and click Detect Displays.
On macOS 27, press Tab in Spotlight. Command-Space, pick a result, and Tab shows what you can do with it without opening anything.
Keep typing while you dictate. On Apple silicon Macs you can fix a word with the keyboard mid-sentence and dictation carries on.
Fn-Q (Globe-Q) opens a Quick Note from any app. In Safari, Share › Add to Quick Note saves the page link with it.
Set a hot corner to Lock Screen. System Settings › Desktop & Dock › Hot Corners. Put Display to Sleep only locks the Mac if your password setting says so. Lock Screen always locks.
Use your iPhone as a webcam and a document camera. Continuity Camera turns an iPhone into a Mac's webcam, as long as both are signed in to the same Apple Account with Wi-Fi and Bluetooth on. Using the iPhone for Desk View adds a view of the desk in front of you: FaceTime shares it directly, and in other video apps you share the Desk View window. It's switched on from the iPhone: Settings › General › AirPlay & Continuity. This is great to use as a 'document camera' to show off things in front of you on the desk.
What's the Mac feature you show people first?