Successful installation of Big Sur Beta4 on two machines, a late 2012 iMac and MacBook Pro 5,2 (C2D Penryn)
iMac installation:
Download Big Sur Beta4 (to download folder), and launch installassistant.pkg; an actual Big Sur Beta4 Installation program will be placed in the Application folder.
Created a USB installer, using the “sudo /Applications/Install\ macOS\ Big\ Sur\ Beta.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume”” command (“MyVolume” would be name of the USB thumb drive.)
Then, utilized Barry K. Nathan’s micro-patcher v 0.0.19 to “prepare” Big Sur Beta4 USB stick for installation (follow directions on Barry’s GitHub site)
Boot into USB thumb drive, and launch the installer; Big Sur B4 installed without problems, other than (expected) lack of WiFi connectivity.
I run jackluke’s “BigSur IvyBridge beta3 prelinkedkernel fix.command.zip” , from Big Sur desktop, rebooted, and had a fully functional Big Sur beta4 installation, including WiFi.
Not sure, whether it was Beta 4 improvement or just fresh install, but I had no problems installing applications or utilities, while previous Beta 3 caused some crashes (?)
MacBook Pro 5,2 (C2D Penryn), installation.
Note, that I used fully functional Catalina installation, present on one partition, to install Big Sur Beta 4 onto same SATA internal disk, but on separate partition. I did not use USB installer.
Download Big Sur Beta4 to Catalina partition. Launch installation.assistant.pkg (should be in download folder), which will place actual Big Sur Installation program into Application folder.
Further installation steps assume, that SIP and “authenticated-root “ are disabled, with nvram set to ‘boot-args=“_no compat_check amfi get_out_of_my_way=1”’
From Catalina desktop, launch Asentientbot’s Hax3.app to initiate installation of Big Sur Beta4 onto separate partition. Let the installer proceed until it is caught in boot-loop, then (on self-reboot) press option key to boot into “drive selection window,” and choose Catalina as your startup disk.
Execute juckluke’s BigSur Penryn beta3 prelinkedkernel fix.command.zip from Catalina desktop, to allow direct-boot back into Big Sur, activate wifi ,and Framebuffer (?)
See post #2529 on page 102 for some further details, and cross-references, on the method used to activate sound ,and a functional “display“ panel. However, to the set of extensions list copied from Catalina, add two extension supplied by jackluke , i.e. AppleHDA.kext and IO80211Family.kext (though I did not actually copy the latter kext to Big Sur)
This post does not have complete details, but I assumed that most people would have installed one of the other Big Sur betas, and would have some familiarity with the process.
Great thank you to all involved in this "holy grail" of computing. If I did not credit someone, it is completely an inadvertent omission.
If someone would like specific details, let me know.
Hope this may be of help.
Just noted jackluke's post #2871; seems my approach is somewhat behind times, if functional.