Only after exhausting the suggestions from the previous Contributor, which should work.
Terminal command below which will only search for any Full Versions of macOS this computer Qualifies to run.
softwareupdate --list-full-installers
It should find the Big Sur 11.7.1 and probably Monterey and Ventura too as the computer does Qualify
Still in Terminal and the next command will download the Full Version of Big Sur 11.7.1. It would place a new application is Applications Folder called " Install Bug Sur "
When ready, just launch it like another application and sold the prompts
softwareupdate --fetch-full-installer --full-installer-version 11.7.1