While exercising as much care as possible when surfing the web is excellent advice, there are times where even stuff gets "placed" on your system. I once had a strange Bitcoin "infection" (nothing came of it), and I certainly don't remember doing anything associated with Bitcoin.
Malwarebytes is very good for finding "ad ware" stuff on your Mac, but not too effective for viruses. An excellent, inexpensive product (you can use it in demo mode for 30 days) is ClamXAV, available from here:
https://www.clamxav.com/
I have used it, and it did catch some "isolated" virus-infected files once. It works very well.
Finally, yes, do perform backups. However, be aware that to recover from a "disaster" with a Time Machine backup is a slow process. This link describes the choices one had for backups:
https://www.mac-help.com/threads/backups-backups-backups.223959/
I myself use SuperDuper!, and it has always been a "life saver" for me. It is especially helpful when I am doing an "upgrade" to a new Mac OS (or sometimes doing an "in Mac OS" upgrade).