High Sierra freezes up on my 2010 iMac 27''

I recently backed up my old hard drive from Time Machine to a new 1 Tb external hard drive Then I installed a new 1 Tb SSD. Using the disk utility, I cloned the new SSD from the Time Machine data on the external hard drive. I increased the memory to 24 GB. My plan was to upgrade my OS from High Sierra to Monterey using the Open Core Patcher. The problem I have now is that I cannot finish downloading the Monterey OS because the computer freezes up. I used the disk utility first aid to determine any problems and all drives look OK except for "Volume could not be unmounted" on the new SSD. The test ends with "Restoring the original state found as mounted." Not sure what that means. Last entry was "Operation successful".

I am using Surfshark VPN which I disconnect. Not sure if that could cause problems.

I have tried to reinstall the High Sierra OS while in Recovery Mode, but the computer freezes up or it says that I have no internet connection to the Apple server . Using my new MacBook Air laptop, I downloaded a Monterey install package from MrMacintoshman on a flashdrive to use, but when I open it on the iMac, it says that it doesn't recognize the file system. Thanks for any ideas.