Hmm. My Dropbox Pro subscription renewal is coming up. Is there an alternative to Dropbox that isn't iCloud or Google Drive? I would like to pay for Tarsnap but I don't understand 250 picodollars / byte-month.
I use SyncThing [0]. It can work without a server if your devices are often up at the same time. Otherwise you can get a small cheap server from the provider of your choice to suit your needs. [0] https://syncthing.net/
It's great for serverless sync between Linux, freeBSD and Windows machines, though - it generally "just works". Didn't try it on macOS or Solaris, never had the need to.