To make the bootable usb installer for the first beta of Catalina, once downloaded to the Applications folder format a 16GB USB as HFS+ Journaled, call it Untitled and run this command in Terminal:
sudo /Applications/Install\ macOS\ 10.15\ Beta.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled
You can then boot up with option key and select the bootable usb.
It is likely the command will change when the second beta comes, maybe to
sudo /Applications/Install\ macOS\ Catalina\ Beta.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled
with "10.15" replaced by "Catalina".
When public release happens, the command becomes
sudo /Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled
sudo /Applications/Install\ macOS\ 10.15\ Beta.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled
You can then boot up with option key and select the bootable usb.
It is likely the command will change when the second beta comes, maybe to
sudo /Applications/Install\ macOS\ Catalina\ Beta.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled
with "10.15" replaced by "Catalina".
When public release happens, the command becomes
sudo /Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled
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