Problems not working with current macOS
My daughter mistakenly upgraded to Big Sur from Mojave. She has a MacBook Air (early 2020), and I can't seem to reinstall Mojave!! Now alot of her programs don't work, and I've erased the HD several times, and I've tried to install a new operation system, but the installer USB is not being read and I get the NO symbol. Her Time Machines are all Big Sur, and now THEY won't even install!!! I am forced to install Catalina--WHICH ALSO HAS PROBLEMS WITH HER PROGRAMS...
Big Sur is BIG PROBLEMS!!! Can anyone help me roll back her machine please?????
[Re-Titled by Moderator]