I have legacy system (ASUS Rampage III / i7 920 CPU) with a working Catalina System running and previously booted by Clover.
Since the last days I have switched to OpenCore and finally now I have a working legacy System booted by OpenCore.
Nearly everything is working but I can't upgrade to Big Sur.
In the System Software-Update Preferences I have downloaded the Big Sur Upgrade and have started the Upgrade Process.
After the first restart a new partition "macOS Install