I've yet to get it to work/update correctly. I've enabled booting from external/usb drives. created the bootable installer on fast thumb drive. restart with option key select Install Big Sur Beta usb drive to boot from Still on beta 2 @mm2012 - can you elaborate on "reboot twice using the OPTION key startup before the actual BigSur beta install will begin"

@NickF81 sudo /Applications/Install\ macOS\ Big\ Sur\ Beta.app/Contents/Resources/createinstallmedia --volume /Volumes/SamsungUSB you have an extra "install macOS" in the application name

So I finally got beta 3 installed. two weird issues. When holding Option to choose boot media, it has you choose "Wireless network" - but I always have wireless off and run wired. I disconnected ethernet and rebooted with Option. selected my wireless network choose Big Sur USB. next I ran into "not enough space" issue even though I had 80gb free (supposedly). found out it was Time Machine local copies. Went to terminal and manually deleted them. Repeated the steps above and after about 30 min and 3-4 auto reboots. I'm on beta 3 I can't guarantee if was my wired vs wireless, but it never worked with wired connection and got it to work with wireless (while disconnecting the cable)

There's several other threads on this. including this one: https://developer.apple.com/forums/thread/655237 It's a "Known Issue" in release notes. Workaround. download the full 12.88GB "update" and use the createinstallmedia command to install it on a bootable usb drive/stick, then reboot from the stick by holding Option down on startup, and choose the "Install macOS Big Sur" volume. Make sure you have at least 36GB free on your main volume to install it.