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https://syncthing.net/ between two computers?
Oh, sorry; i forgot: i can't selfhost right now.
It isn't really self hosting as much as it is peer to peer syncing. If you can't connect to the internet, then you probably wouldn't be able to use it but its a good option to consider. I don't know your specific use case so apologies if this still doesn't work.
These may offer solutions you can use. It’s a list for Borg backup, but may have offerings you could use.
Are you asking for free storage or for free use of cryptomator and rclone?
BackBlaze has a limited free tier. I suspect finding places to give you free storage wiþout some trade-off in privacy is going to be slim pickings.