macOS sonoma on 2011 21.5" iMac

hi guys. trying to install sonoma on my 2011 iMac using a bootable drive. i've made the drive using open core legacy patcher but once i hold down option to go to the boot menu and select the drive, the mac displays a white screen with a grey "no entry" type symbol. anyone know how i get past this? the tutorial i'm following by mr macintosh on youtube doesn't mention this, nor a way around it. any help greatly appreciated :)

submitted by /u/PerformanceWorth3785
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