There are unknown names in your Keychain this is totally normal on every system. As stated the octagon file is part of the OS security and should not be removed. Modifying keychains is only going to give you problems with your Mac requiring a Factory Reset.
Norton 360 is not recommended to install. You will see false claims of security issues. This is how they keep themselves relevant so you believe you need their software and will continue to pay more for it. Here are just 3 previous articles from this support forum:
https://discussions.apple.com/thread/254569992
Norton 360 deluxe - Do or don't? - Apple Community
Norton 360 Mobile Security - Apple Community
Your Mac has built in protection from viruses and continually gets Security Update. To make sure you keep your Mac safe, do not install any Cleaner App or Anti-Virus software. Along with that, do not install from a Safari notification saying you have a virus or from a pop up on a website. These are known scams.
More importantly is keeping your Apple ID password safe and avoid phishing messages. For more information about these:
Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support
If you do think that your Apple ID has been compromised, then you can follow this support article:
If you think your Apple ID has been compromised - Apple Support
When using Safari, do not allow Notification or Pop-ups from every site you use. This is the source of common problems and in most cases, you do not need them.
Other than that, enjoy your Mac and try not to be looking for problems you do not have. If you do experience a specific problem when using it, feel free to create a new question with your concerns and issues you are having. At this point, there is nothing you should be concerned with from what you have posted.