Best Apps for cleaning Imac and Virus protection

First, there is no reason to ever install or run any 3rd party "cleaning", "optimizing", "speed-up", anti-virus, VPN or security apps on your Mac.  This documents describe what you need to know and do in order to protect your Mac: Effective defenses against malware and other threats - Apple Community and Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support.  

There are no known viruses, i.e. self propagating, for Macs.  There are, however, adware and malware which require the user to install although unwittingly most of the time thru sneaky links, etc.   

Anti Virus developers try to group all types as viruses into their ad campaigns of fear.  They do a poor job of the detecting and isolating the adware and malware.  Since there are no viruses these apps use up a lot of system resources searching for what is non-existent and adversely affect system and app performance.

There is one app, Malwarebytes, which was developed by a long time contributor to these forums and a highly respected member of the computer security community, that is designed solely to seek out adware and known malware and remove it.  The free version is more than adequate for most users.  

But MalwareBytes is a scanner for malware, not viruses

A virus is malware. Malware is short for malicious software. All of these are malware.

Virus

Trojan

Worm

Those are the most basic categories. Everything else is a subset of one of these three.

There are no Mac viruses. Zero. A virus is self-propagating software. They require no user interaction to infect one file or drive after another. The only known Mac worm was Oompa-Loopa. Also known as Leap-A. It was patched against over a decade ago.

Everything else (and there are a lot of them) is a Trojan. Those are any type of software that requires the user to do something to get them on your Mac. They can't get there by themselves.

AV software is useless. Literally. There are no viruses to look for, and since they cannot know what software you're going to install or run until after the fact, they can't stop you from installing or running a Trojan.

Anything you see like that - literally - all of it, is a scam. No one anywhere can see what's on your computer through a web browser.

The reason is came back is Safari reloads the last tabs that were open. To prevent that, hold down the Shift key while launching Safari. That tells it to ignore all previously open sites.

What I use is: macOS - Security - Apple

Apple Platform Security - Apple Support

Protect your Mac from malware - Apple Support

You had allowed websites to send notifications and that website had a spam notification. Here's how to get rid of it - in Safari's Website/Notifications settings:

Obviously just macOS ... that's ALL the AV you need. But MalwareBytes is a scanner for malware, not viruses, so it's good to use if you actually have malware or wish to test for it.

Those software is not nessecary. If you have or suspect malware, malwarebytes is fine but further there are no security or cleaning tools needed. macOS does all that for you

Have no first hand knowledge of the Duck Duck Go browser. I prefer Safari as it's integrated into the system and its features.