Go to System Preferences > Software Update on your Mac.
Advanced users can use the command softwareupdate --fetch-full-installer --full-installer-version 11.1 . Key Features of Version 11.1 (20C69) advertisement macOS Big Sur 11.1 (20C69) Free Download
To ensure a safe installation, you should only download macOS Big Sur through official Apple channels: Go to System Preferences > Software Update on your Mac
Apple provides all macOS operating system updates at no cost. If you see an advertisement or a third-party site asking for payment for this specific download, it is likely a scam or a "pirated" distribution that could contain malware. advertisement macOS Big Sur 11.1 (20C69) Free Download
This version was the first major point release for Big Sur and introduced several improvements: How to download and install macOS - Apple Support