Syncthing solves a large part of syncing data between devices using your own VPS, server(s), etc. If your VPS provider goes out of business, you can then just fire up a new VPS and hook it back up to your local machine(s).
Cryptomator [1]. Cross-platform, allows you to encrypt your data in the cloud, and access it transparently.
Thing is, like Syncthing, it lacks a collaborative feature. Nextcloud has it, but only if you have the Nextcloud accessible (I want to host only on LAN). Something like IPFS (or Tor) is a solution to such problem.
there's also resilio sync that gives you the option have the node/folder on your vps be encrypted. hopefully syncthing will add that feature at some point in the future
I have been considering spending more money than I should finding someone on a freelancer site to add the untrusted node / encrypted file transfer but don't give a certain node the key to decrypt the file support, that is the number one missing feature for syncthing for me.
It would unlock scenarios like share your files with me and I'll share files with you and neither of us will know the others files unless your house burns down in which case you can get your files back just by hookin the sync back up with the encryption key pulled from your password manager.
I'm on Android so it works, but I also used Nextcloud for some time and had issues with it "forgetting" about the data folder, so I had to re-create it every time it happened. I wasn't happy about that.
Syncthing solves a large part of syncing data between devices using your own VPS, server(s), etc. If your VPS provider goes out of business, you can then just fire up a new VPS and hook it back up to your local machine(s).