I used an OpenCore Legacy Patcher to install macOS Monterey on my old mid-2011 iMac. I think that I must have deleted data from the hard drive that allowed diagnostics. I long pressed the D key while booting up my Mac first but failed to enter the Diagnostics Mode. Then I tried the Option - D keys while starting up my iMac for Internet Diagnostics, it just stayed at the loading screen (the globe) right after you entered your Wi-Fi password for all night(12 hrs). So, I want to know how can I get that Diagnostics Mode.
How’s the condition of your Wi-Fi? If your Wi-Fi is poor, it will block your Mac from entering the Diagnostics Mode. You can try to reboot your router and then reconnect the Wi-Fi or change to connect to another Wi-Fi. Then use Option - D again while restarting your Mac to enter the Diagnostics Mode.
The old mid-2011 Mac doesn’t support macOS Monterey by default. If you install macOS Monterey on your iMac with OpenCore Legacy Patcher), your Mac may perform abnormally. That may be the cause why you can’t enter the Diagnostics Mode. If you want to use the Diagnostics Mode, you’re suggested to downgrade your Mac to the macOS that’s compatible with your Mac.
Maybe that’s the case. I’ll try to downgrade my Mac to a compatible system.