You've got a few options. If you want it stored privately for free, you could store it with GitLab (or even github these days I guess). Or any other public cloud provider (NextCloud, dropbox, a server you have for a website).
Personally, though, I don't do any of those—I store the primary copy on a home server, and sync that to my laptop, my wife's laptop, and each of our phones. True, we can only sync when we're at home—but that's basically every day.
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