Your 'build model year' seems to be listed on this Support page:
• macOS Big Sur is compatible with these computers - Apple Support
https://support.apple.com/en-us/HT211238
• How to upgrade to macOS Big Sur - Apple Support
https://support.apple.com/en-us/HT201475
Does your MacBook Pro have Mojave or newer macOS installed?
See Step 4, in above ^ read to see if this helps install Big Sur in your Mac.
Download Big Sur macOS11.x:
"If you're using macOS Mojave or later, get macOS Big Sur via Software Update:
Choose Apple menu > System Preferences, then click Software Update.
~ Or use this link to open the macOS Big Sur page on the App Store:
Get macOS Big Sur. Then click the Get button or iCloud download icon."
[Perhaps Catalina could be better suited, it's rather new still & secure?]