The best way to keep data is to keep copies of it. Copying your data is what backing up is all about.
Given that so many people do many things across so many devices it’s hard to give good advice for everyone.
Personally, I use a combination of places, apps, and services to provide myself a variety of backups.
On my Macs I use Arq to back up hourly to my 1TB Dropbox personal account with a budget of 700GB and sometimes I run a full backup to an S3-compatible bucket on my synology NAS via a Minio docker container running on there. I don’t use my Dropbox for much and I don’t back up my entire computer to there. I ignore anything that I keep downloaded simply to have a copy.
I also use Backblaze, but I’m not particularly excited by it. I’ve never really needed to use it and I wonder if my current backups aren’t already good enough. Dropbox is not expensive and gives me geo-redundancy while my NAS with RAID5 does a more complete backup