Late 2012 iMac; Error erasing USB to create installer?

There’s no error number, so I can’t figure out what’s wrong?? I’m trying to update a late 2012 iMac (iMac13,1) that is still running OS-X. End goal is Sonoma, but have to install High Sierra first.

Running OpenCore 2.4.1. Using a 32GB USB. I’ve erased and reformatted it half a dozen times. I’ve checked permissions under settings. I cannot find a clear answer. What’s the solution??