"Critical virus alert Virus detected!" pop up on my iMac

As you mentioned - My antivirus program finds no virus. Sometimes the pop up says that my iCloud account has been hacked. How do I get rid of this pop up malware since Virus One and Cleaner One Pro are not eliminating it?

You don't need any anti virus / or cleaner that is installed in Mac , click on finder > applications select them and move to trash , restart the Mac and empty the trash .

See Install and uninstall apps from the internet or a disc on Mac - Apple Support

Also , clear all history and website data Clear your browsing history in Safari on Mac - Apple Support

If you are using safari for browsing , click on the url link and use the settings as per screen shot .

See the articles Change Websites settings in Safari on Mac - Apple Support

Customise settings for each website in Safari on Mac - Apple Support