Simple steps to get Android File Transfer to recognize your phones and tablets on macOS (including 10.13 High Sierra)

Android File Transfer on macOS.md

Reports of Failures with macOS/Mac OS X and Android File Transfer.app

A quick search on DuckDuckGo or Google when you encounter the "No Android device found" dialog from the 2012 (latest) version of Google's Android File Transfer.app will tell you about multiple others seeing the same problem. Too few (none?) have the following solution.

Launch Order Matters

Do the following in order to have Android File Transfer.app show your Android phone or tablet's file contents.

1. Connect your Android phone or tablet to your Mac (via USB-C, USB 2/micro-USB, or an adapter between the two, as necessary)
2. Leave your device in "USB charging this device" mode
3. Launch your Android File Transfer.app, and wait for "No Android device found"
4. Switch your device to "Transfer files" mode
5. You now have Android File Transfer.app displaying your device type along the top of its window, and your folders in the main pane of the window
6. Transfer to your hearts content

Thanks for the solution, Richard!

Note for others: I have activated the file transfer mode on my phone already earlier on windows. When I switched to macos and installed the app, it still didn't work. I had to change back to USB charging this device first, then follow the guide.