These last few years I have had to reinstall the macOS (mostly in Catalina) several times from Recovery Mode over the Internet. It is a bit tedious, but I am very glad it is there to keep my Mac going during difficult times. It appears that when you run Recovery Mode on Intel Macs Apple installs macOS Catalina! There is no Recovery install for macOS Big Sur on Intel Macs. Apparently, this is a server problem and Apple is working on it. I hope they get it fixed soon. In the meantime, it is not a bad idea to have a clone of your Big Sur system.