4. Set Individualized Read Receipts
If you want to turn on or off read receipts just for one person in Messages, you can do that. All you need to do is click on Details beside that person’s name, and turn Send Read Receipts on or off.

5. Filter Unread Messages in macOS Mail
As another hidden macOS feature, the Mail app now allows you to filter your unread messages. At the top of the messages pane, you’ll see a circle with an upside-down triangle. Just click on that little button, and Mail will filter your email, showing you only unread messages.

Bonus Tip: Quick Look at Documents and Images
As one last tip, the Finder has a Quick Look feature. After you’ve single-clicked on a document, image, or other types of files, press the space bar on your keyboard. A quick preview of that file will show up, along with the option to open it in the correct app.

What is your favorite hidden macOS feature? Tell us about it in the comments.
Quick Look is something I use all the time. Once, I even watched an entire TV episode by using it. But even more kewl; if you have saved to your desktop the URL of a specific web page, it will open with Quick Look also–even when the web page has motion graphics or video!
My addition. Quick Look also works in Open and Save dialogs.
It has been my experience that too few songs have lyrics available through iTunes or Music. I try to find them on one of the lyrics website, copy and paste them to the song using Use Custom Lyrics. On more than one occasion I have transcribed the lyrics.