Can my Mac Pro 2011 late upgrade to macOS Big Sur?

You may also look into and study short-list of Apple's downloadable installers

which arrive online via their servers. ~ And in turn, these get the files your Mac

needs to install the appropriate macOS. Expect you'd need a good backup too.

• How to get old versions of macOS - Apple Support

https://support.apple.com/en-us/HT211683

macOS Mojave 10.14 hardware requirements

+ downloadable installer (use Safari browser)

macOS Mojave 10.14 can upgrade High Sierra, Sierra, El Capitan, Yosemite, Mavericks, Mountain Lion

NO - this guide will show you what OS Systems can work with which Mac's. For your Mac Mojave is as far as you can go.

https://eshop.macsales.com/guides/Mac_OS_X_Compatibility