Big Sur via Opencore on iMac Early 2009 on stock HDD and 4gb ram! Works amazing ! : r/BigSurPatcher
Apple releases list of Macs that will run macOS Big Sur | AppleInsider
Success! Big Sur install with OCLP on Mac mini 2009 3,1 with 6GB of ram and SSD. Running okay but does slow down with a few windows open. Recommended to upgrade to