There are many ways of doing backups. Be careful of the difference between a sync service like OneDrive and a backup service.
I follow the 3-2-1 backup philosophy: three total copies, where two are local and one is offsite.
I have my notes on my Mac. I use a macOS automation tool called Keyboard Maestro to regularly copy those notes onto an external drive. And I use the (paid) Backblaze service linked above to keep an off-site backup of my entire Mac and the external drives with them.
So, basically, copy your notes to a different disk on a regular basis, and copy them into a backup service on a regular basis. You can use OneDrive for the latter, but—importantly—you shouldn’t actively work on your notes in OneDrive if that’s your backup solution. (This is because if you make a change to the notes that you want to roll back, you can’t use your OneDrive “backup,” because it will have synced the change you made!) So, to restate, you can use a service like OneDrive as a backup, but do so by copying your files into OneDrive, not by working on your files while they’re being synced with OneDrive.
It is a bit nuanced, but the specifics are important!