Cannot reinstall operating system because of locked disk- high sierra

[oscar_fizz]

Hi, I got a new Mac mini and migrated my 2017 iMac over successfully. The iMac will be going to my mom and I followed some instructions to log out and erase the hard drive (minus the Time Machine back-up, sigh).



First I ran into this error "The Recovery Server Could Not Be Contacted", but was able to fix it with this video:

So the server can now make contact to reinstall High Sierra, but when I click on the hard drive I get the error "This disk is locked"



Things I have tried:

• Restarting with:

cmd + option + shift + R

Cmd + R

Cmd + option + R

Alt

• Running first aid in disk utility- successful
• Partitioning- error "Operation failed"
• Unlocking from the terminal per: diskutil apfs unlockVolume diskXsY. The response was it was already unlocked.

I don't know what the issue is and have tried multiple things from various forums, so at this point any practical help would be so much appreciated! Is there something I can upload from a thumb drive or........?



Thank you!





Attached are some screen shots.

 

[Bigwaff]

When in Disk Utility, make sure you select menu View > Show All Devices. Then pick the top most node in the device tree in the right panel, the device tree for "Untitled". This is the node you want to perform the Erase on. Choose a single partition if it is not the default.