I easily installed macOS Big Sur 11.0.1 (20B29) in my 27'' iMac (Late 2013 - fully Apple BTO improved) and everything works perfectly. My iMac is equipped with a Fusion Drive which I intend to separate and replace the mechanical HDD with a 2TB Crucial MX 500 SSD.
So, if you have a 27-inch iMac from late 2013, rest assured it's perfectly suited to Big Sur.
I add some details to facilitate the transition, without risking anything, proceeding to do everything BEFORE disassembling the iMac to change the original HDD with the new SDD.
1) I used Micropatcher as suggested by default (without additional flags) to patch the USB Key with Big Sur. I created the USB Key by createinstallmedia.
2) I connected the Crucial SSD via an external USB 3.1 adapter and formatted it as APFS.
3) I restarted the Mac from the USB Key patched with Micropatcher and after having first booted from the "EFI Boot" unit I turned the iMac back on and installed Big Sur from USB key to the external Crucial SSD that I named "Macintosh SD".
The Mac has been running great from two days. I'm stressing him out and he doesn't crash and never freezes.
In the meantime, Finder see perfectly the internal Fusion Drive with Catalina and I take the opportunity to copy my many Internet Accounts to Big Sur (by copying the files contained in My_Home/Library/Accounts/ of Catalina's disk to the identical folder of Big Sur disk.
This worked great right away and after a Logout/Login all of my Internet Accounts appear in Big Sur's System Preferences
Next, I will pass the contents of My_Home/Library/Mail/, the contents of My_Home/Music/Music folder, the Photo's library and everything in between.
At the end, when I have verified with certainty that I have passed everything on Big Sur and that it works fine, I will open the iMac and replace the HDD with the SDD in which Big Sur is.
It was simple and fun 😉
NOTE: in my opinion, maybe Big Sur could also be installed in the Fusion Drive; mine is the 1,128 TB one with 128GB SSD. If I have time I will try to do a clean installation to the Fusion Drive, from zero, to make a comparison with the external SDD; after all, if it goes wrong, I intend to proceed with the replacement of the HDD anyway.