Hello!  Help me please,  I have got MacBook Air 2018 with OS Catalina, but today I tried to install the new beta OS Big Sur.  I didn’t make any backup for my system and having installed the Big Sur, just like in 10 minutes, I decided to reinstall Catalina.  Then after reboot Mac with cmd+R, I erased disk and OMG. Then I attempted to reinstall the Big Sur, so I rebooted my MacBook and after that I was witnessing the rotating globe for some 10 minutes.  As the globe ceased rotating I saw window with MacOS Utilities, and there we go…  When I press the reinstall button (AND ITS NOT CATALINA, BUT MOJAVE), it takes a long time for it to be installed, (while 6.08 GB of Mojave are downloading) and then the installation fails (2 minutes remaining) Mac reboots itself.  I’ve tried to erase disk in various ways — not only volumes, but whole disk.  Now I don’t know what to do and maybe photos there will - https://discussions.apple.com/thread/251774873 help.  And I repeat again firstly was Catalina -> Big Sur -> erase disk -> and now it’s only showing Mojave. By the way, Mojave notifies, that  it may only be installed on APFS, so I can’t choose extended journal for disk. I have already written about this problem here - https://discussions.apple.com/thread/251774873