I have an update regarding my 2009 21.5" iMac
It now is back to life as a Ubuntu Linux machine.
I’m pissed because I brought it to a third-party to look at it, thinking the issue was a hardware one. All he did was re-install macOS High Sierra again and like an idiot I paid $90 for this service.
Conclusion
I didn’t finish setting up macOS and I put Ubuntu Linux instead. I also used balenaEtcher to make a Ubuntu Linux install flash drive.