Whatever you do, avoid Norton or McAfee like the plague!
They're resource hogs and generally decrease system performance and usability by a good 30-50% in my experience. You can have a 10-15y/o PC, with the right OS and hardware choices, that runs perfectly fast and usable. Add Norton or McAfee to the mix and things become extremely annoying and painful.
Malwarebytes is one option that's worked quite well for me for some time. Some others I haven't used in quite a few years, but at least in the past used to be good (not sure how they are now) are
ESET and
Kaspersky. Considering the current global conflict and Kaspersky's origin, I am unaware of whether there are current concerns over using their software or not.
Some or most of the above (except Malwarebytes) also work on Linux. That said, one app you'll see most frequently recommended for antivirus on Linux is
ClamAV. It's free and open source, which is great. Only downside is it takes a bit of setup maybe a bit beyond what the average user might want to deal with.
Although some Linux distributions may be able to install it through the graphical package manager/app store, more commonly people install it through the terminal as it is a terminal-based app. There are some third party GUI apps for it but, this may be beyond the scope of what many here are willing to deal with setting up.
ClamAV is not quite the full-featured antivirus app like some of the others, so just be aware. It's mainly used for running scans of files already on your system. I don't believe it gets used for things like real-time scanning of traffic or some of the other real-time type protections like some of the other apps.
If you do like to tinker, simple tutorials are more than sufficient to get up and running with ClamAV in a few minutes. It is also available for Windows as well, though I've never used it on Windows and can't comment on that.