Erasing HDD prior to Sale - Can’t Reinstall macOS

Hello - I’ve recently sold my 2017 iMac, so I’ve been following the steps to backup and reset my computer before shipping it out (hopefully today). I had no issues with backup, but am concerned about how I deleted the HDD. In Disk Utility, I deleted the Macintosh HDD and reformatted to APFS. Now when going to reinstall macOS High Sierra, I am not able to select a disk for install.

Reverting back to Disk Utility, the HDD is now named “Container disk 3” with an OS X Base System mounted as a disk image. First Aid runs on Container disk3, but does not seem to change anything. I am not able to partition, erase, restore or mount Container disk 3 given “erase process has failed”.

I am worried that I may have bricked my computer, so please let me know if there are any tips. I have my old computer backed up on an external HDD, but seems like internal HDD is having issues. When it reboots, it goes to the spinning globe icon and downloads the recovery files.