Click the Apple menu () in the top-left corner and select About This Mac .
While your serial number is not as sensitive as a password, you should still be careful about where you post it publicly. apple specs lookup by serial number
If you have an older Mac, looking up the Model Identifier tells you exactly which OS it can run. You might find your "2015 MacBook" can actually run macOS Monterey, or conversely, that your old iMac stops at Catalina. Click the Apple menu () in the top-left
Several third-party websites offer Apple serial number lookup services. Some popular options include: apple specs lookup by serial number