OCLP weird bug?

So I used it to upgrade an old Mac Pro 6,1 and was having some issues. I decided to just stay with Monterey as it is the last supported OS.

I used a bootable USB drive and all seemed fine and dandy. Software update then asked if I wanted to upgrade to Sonoma, an unsupported OS for this machine.

I’m not the greatest when it comes to non basic things with a Mac, as I’ve not really done much with formatting etc. But I do know more about windows in that sense.

Do I need to do something like an Fdisk and completely wipe the partitions that disk utility doesn’t do when you use a bootable installer? I thought the installer did this automatically but obviously something was left behind to tell it to download Sonoma.

I read somewhere about the EFI partition but I have no idea where to go to actually SEE if it is still there, as there was nothing shown using disk utility. I did not want to go and blow up the whole SSD just in case the bootable wouldn’t fix everything and that is probably what I need to do. There is a 1GB partition that I thought was needed for Disk Utility but maybe it isn’t.

Any help would be appreciated. Thanks