What @SheriGR said. I had a tragic hard drive loss over a decade ago and I'm still paranoid. (I'm still traumatized and will be for life!)
The pro backup rule is if the data is important, you want three copies in two different physical locations. (You get to decide what's important to you, data-wise.) Three copies--one of my ex-boyfriends, back in Ye Olden Daze, had a single copy of media to back up his hard drive and his hard drive died mid-backup, so the media had an incomplete backup, aka no backup. *sad trombone* Your backup location can also fail. And if they're both in the same building, the building can burn down with your data and the backup in it. A cloud service counts as a different physical location.
I have a copy of my Sims 4 folder on my NAS, and keep a second copy of just the saves on a thumb drive. You could also use OneDrive/Google Drive/Dropbox/the cloud service of your choice.
I also do a full image backup of my hard drive nightly. Since I've started doing that, I've had a hard drive death and I just popped in a new drive and did a restore and it was like nothing ever happened. I use Acronis; it does your full Windows install and everything and has saved me more than once.
I mean, each person should decide how hard-core they want to be and what level of bitrot they're comfortable with, but just dumping your Sims 4 folder into Dropbox every night might be good enough.