iMac stalled during reboot

A friend recently gave me a 2011 iMac running one of the latest OS versions. I forgot to write down which one but I know it is newer than High Sierra. The computer was running fine: I was able to launch various programs and connect to the internet.

My friend was the Admin but gave me her password so I could set up a new account for myself before deleting hers. I did that and then added myself an Admin. (I did not delete her as an Admin.) After I made those changes a box appeared saying that I had to restart in order for the changes to become effective.

I did a soft restart from the Apple menu. The result was a gray screen with the Apple logo and a progress bar that moved fairly quickly at first, than slowed down about 3/4 of the way across. Several hours later the progress bar is all the way across but nothing else has happened. The computer is frozen.

I know about Safe Mode but I can't do another Restart because I have no Apple menu. Should I force it to quit using the power button and then restart? Is there anything else to try? And did I do something while setting up my account that I shouldn't have?

Thank you for any and all suggestions. Right now I have a big silver doorstop on my counter. ☹️