I've been using Syncthing for years: https://syncthing.net/

It's entirely P2P, so no 3rd party hosting of your files, no trusting someone's crypto/update schemes, or having to set up your own servers (although you still can easily add it to a VPS if you want offsite). There's also a nice mobile app:

https://play.google.com/store/apps/details?id=com.nutomic.sy...

You can also securely share directories with another person who uses Syncthing, I've found autosync directories are easier than using something like Airdrop for sharing photos with family.

I don't know much about them, but Sync https://www.sync.com seems to be in this space.

Has a 5GB free tier, higher tiers cheaper than dropbox. Based in Canada if that matters.

I've seen a HN poster promote filestash.app which looks like it's either self-host or hosted. I guess you might have to add in something like Spideroak, Backblaze, or tarsnap if you want to self host + backup.

Or Syncthing as others have pointed out.

I'm still thinking which is best.

Nextcloud is a wonderful bit of FLOSS, been using it for years now.