Sync is the way to go. If you want to self-host, syncthing is very good. From a security perspective, Steve Gibson, host of Security Now podcast and all around encryption & security expert did a review of the landscape of available syncing solutions and settled on syncthing though he also recommended sync.com. See Episode 734.
Filen.io is E2EE and 10 GB for free. a little under $40 for 100 GB lifetime license. Nice thing about this service is you can set up individual syncs per computer folder to cloud folder and every individual sync can have its own setup. One of the nice setups is “local backup”, whereby everything is synced but local deletes are ignored. They also offer file versioning.
I am a new obsidian user so I don’t have much experience with syncing. Obsidian’s syncing service works well but sync dot com would be more flexible for me (sync other stuff as well as obsidian; have archived files that are online only). From what I’ve heard, using iCloud to sync obsidian vaults is sometimes wonky and may not sync as quickly as the other synching solutions.
I’ve done this in the past. Sync is fast and easy. While Sync is great, I don’t wildly throw personal or financial documents into sync. Some aspects of it are open, but it is a bit of a black box. I’ve reached out to support on a few topics, and while they have responded getting deep technical answers is impossible; don’t need to know trade secrets here, just how it works.
If comparing to other services it’s closer to iCloud Drive than Google Drive or Dropbox. No/Hidden API (Slack, O365, etc.). Does have version control and is fast and reliable. I believe the client is open source (don’t quote me on that), but aside from that very hard to get 3rd party audit data etc. Keeps me from making it core part of my workflow.