Buligi wrote:
Hello, I am trying to install macOS Big Sur on Mac Book pro 15 retina using a bootable usb drive, but it shows support.apple.com/Mac/startup with a crossed circle. What could be the problem?
[Re-Titled by Moderator]
MacBook Pro 15″, macOS 10.14
Not enough information.
if you are running " MacBook Pro 15 macOS 10.14" you can not go backwards unless you completed erase reformat the drive predicated the Mac ran that macOS version or early when shipped new—this depends on the exact Mac
macOS Big Sur - Technical Specifications - Apple Support

Erase and reformat a storage device in Disk Utility on Mac View>Show All Devices
Erase and reformat a storage device in Disk Utility on Mac - Apple Support
erase the top most ( parent drive ) not the container level, not the Volume level.